Trigger frames adapted to packet-based policies in an 802.11 network

ABSTRACT

In 802.11ax networks with access points, a trigger frame offers scheduled and random resource units to nodes for data uplink communication to the access points. To make more effective the usage of the network, the access point may design the trigger frame to force the nodes to send some categories of data. Resource units may be defined in trigger frames to be dedicated to small packets or to some access category data. Adjusting the time length of the resource units helps restricting the type of data that can be conveyed by the resource units. Also, using various frequency widths for resource units in the same trigger frame helps reducing padding in the resource units when various traffic types coexist.

FIELD OF THE INVENTION

The present invention relates generally to wireless communicationnetworks and more specifically to the random allocation for Uplinkcommunication of OFDMA sub-channels (or Resource Units) forming forinstance a communication composite channel. One application of themethod regards wireless data communication over a wireless communicationnetwork using Carrier Sense Multiple Access with Collision Avoidance(CSMA/CA), the network being accessible by a plurality of node devices.

BACKGROUND OF THE INVENTION

The IEEE 802.11 MAC standard defines the way Wireless local areanetworks (WLANs) must work at the physical and medium access control(MAC) level. Typically, the 802.11 MAC (Medium Access Control) operatingmode implements the well-known Distributed Coordination Function (DCF)which relies on a contention-based mechanism based on the so-called“Carrier Sense Multiple Access with Collision Avoidance” (CSMA/CA)technique.

The 802.11 medium access protocol standard or operating mode is mainlydirected to the management of communication nodes waiting for thewireless medium to become idle so as to try to access to the wirelessmedium.

The network operating mode defined by the IEEE 802.11ac standardprovides very high throughput (VHT) by, among other means, moving fromthe 2.4 GHz band which is deemed to be highly susceptible tointerference to the 5 GHz band, thereby allowing for wider frequencycontiguous channels of 80 MHz to be used, two of which may optionally becombined to get a 160 MHz channel as operating band of the wirelessnetwork.

The 802.11ac standard also tweaks control frames such as theRequest-To-Send (RTS) and Clear-To-Send (CTS) frames to allow forcomposite channels of varying and predefined bandwidths of 20, 40 or 80MHz, the composite channels being made of one or more channels that arecontiguous within the operating band. The 160 MHz composite channel ispossible by the combination of two 80 MHz composite channels within the160 MHz operating band. The control frames specify the channel width(bandwidth) for the targeted composite channel.

A composite channel therefore consists of a primary channel on which agiven node performs EDCA backoff procedure to access the medium, and ofat least one secondary channel, of for example 20 MHz each. The primarychannel is used by the communication nodes to sense whether or not thechannel is idle, and the primary channel can be extended using thesecondary channel or channels to form a composite channel.

Sensing of channel idleness is made using CCA (clear channelassessment), and more particularly CCA-ED, standing for CCA-EnergyDetect. CCA-ED is the ability of any node to detect non-802.11 energy ina channel and back off data transmission. An ED threshold based in whichthe energy detected on the channel is compared is for instance definedto be 20 dB above the minimum sensitivity of the PHY layer of the node.If the in-band signal energy crosses this threshold, CCA is held busyuntil the medium energy becomes below the threshold anew.

Given a tree breakdown of the operating band into elementary 20 MHzchannels, some secondary channels are named tertiary or quaternarychannels.

In 802.11ac, all the transmissions, and thus the possible compositechannels, include the primary channel. This is because the nodes performfull Carrier Sense Multiple Access/Collision Avoidance (CSMA/CA) andNetwork Allocation Vector (NAV) tracking on the primary channel only.The other channels are assigned as secondary channels, on which thenodes have only capability of CCA (clear channel assessment), i.e.detection of an idle or busy state/status of said secondary channel.

An issue with the use of composite channels as defined in the 802.11n or802.11ac (or 802.11ax) is that the 802.11n and 802.11ac-compliant nodes(i.e. HT nodes standing for High Throughput nodes) and the other legacynodes (i.e. non-HT nodes compliant only with for instance 802.11a/b/g)have to co-exist within the same wireless network and thus have to sharethe 20 MHz channels.

To cope with this issue, the 802.11n and 802.11ac standards provide theability to duplicate control frames (e.g. RTS/CTS or CTS-to-Self or ACKframes to acknowledge correct or erroneous reception of the sent data)in an 802.11a legacy format (called as “non-HT”) to establish aprotection of the requested TXOP over the whole composite channel.

This is for any legacy 802.11a node that uses any of the 20 MHz channelinvolved in the composite channel to be aware of on-going communicationson the 20 MHz channel used. As a result, the legacy node is preventedfrom initiating a new transmission until the end of the currentcomposite channel TXOP granted to an 802.11n/ac node.

As originally proposed by 802.11n, a duplication of conventional 802.11aor “non-HT” transmission is provided to allow the two identical 20 MHznon-HT control frames to be sent simultaneously on both the primary andsecondary channels forming the used composite channel.

This approach has been widened for 802.11ac to allow duplication overthe channels forming an 80 MHz or 160 MHz composite channel. In theremainder of the present document, the “duplicated non-HT frame” or“duplicated non-HT control frame” or “duplicated control frame” meansthat the node device duplicates the conventional or “non-HT”transmission of a given control frame over secondary 20 MHz channel(s)of the (40 MHz 80 MHz or 160 MHz) operating band.

In practice, to request a composite channel (equal to or greater than 40MHz) for a new TXOP, an 802.11n/ac node does an EDCA backoff procedurein the primary 20 MHz channel. In parallel, it performs a channelsensing mechanism, such as a Clear-Channel-Assessment (CCA) signaldetection, on the secondary channels to detect the secondary channel orchannels that are idle (channel state/status is “idle”) during a PIESinterval before the start of the new TXOP (i.e. before the backoffcounter expires).

More recently, Institute of Electrical and Electronics Engineers (IEEE)officially approved the 802.11ax task group, as the successor of802.11ac. The primary goal of the 802.11ax task group consists inseeking for an improvement in data speed to wireless communicatingdevices used in dense deployment scenarios.

Recent developments in the 802.11ax standard sought to optimize usage ofthe composite channel by multiple nodes in a wireless network having anaccess point (AP). Indeed, typical contents have important amount ofdata, for instance related to high-definition audio-visual real-time andinteractive content. Furthermore, it is well-known that the performanceof the CSMA/CA protocol used in the IEEE 802.11 standard deterioratesrapidly as the number of nodes and the amount of traffic increase, i.e.in dense WLAN scenarios.

The number of large collisions and associated retransmissionssubstantially increases as the network density increases.

A problematic situation regards so-called “small packets”, i.e. MACpackets that intrinsically suffer from an important overhead (relativeto the amount of payload data) due for instance to the MAC header, tothe waiting times to access the wireless medium, etc. The higher thenumber of small packets, the higher the loss of network bandwidth due tocorresponding overhead, and thus the higher the number of collisions andretransmissions associated with small packets.

In addition, the problematic situation is getting worse since, althoughthe overhead due to the MAC header is fixed, the waiting time increaseswith the number of nodes (the medium to access is shared between ahigher number of nodes) and with the number of collisions.

The well-established traffics (or scheduled traffics managed by the AP)may thus suffer from small packets conveyed on the network.

However, the scheduled traffics are not the principal ones in a basicservice set (BSS) made of the AP and its registered nodes.

For the nodes to coordinate together, a new hybrid coordination function(HCF) has been introduced that includes two methods of channel access:HCF Controlled Channel Access (HCCA) and Enhanced Distributed ChannelAccess (EDCA). Both EDCA and HCCA define Traffic Categories (TC) toadjust QoS (Quality of Service) support by differentiating andnegotiating node service parameters. For instance, an email could beassigned to a low priority class, and Voice over Wireless LAN (VoWLAN)could be assigned to a high priority class.

Four Access Categories are defined:

AC_BK is the lowest priority for background data,

AC_BE is the next priority for best-effort data,

AC_VI is the priority for video applications, and

AC_VO is the priority for voice applications.

Each access category owns substantially two traffic classes as definedin the IEEE standard 802.11. In the document below, traffic classes andaccess categories are indifferently used to designate the same idea.

These QoS traffics are by essence unfair. Collisions and retransmissionsare exacerbated in dense environments like the ones addressed by802.11ax, thus conducting to poor efficiency of the wireless medium,

In this context, multi-user transmission has been considered to allowmultiple simultaneous transmissions to/from different users in bothdownlink and uplink directions. In the uplink, multi-user transmissionscan be used to mitigate the collision probability by allowing multiplenodes to simultaneously transmit and to improve network capacity bymutualizing the overhead (header, waiting times . . . ) over the MACpackets.

To actually perform such multi-user transmission, it has been proposedto split a granted 20 MHz channel into sub-channels (elementarysub-channels), also referred to as resource units (RUs), that are sharedin the frequency domain by multiple users, based for instance onOrthogonal Frequency Division Multiple Access (OFDMA) technique.

OFDMA is a multi-user variation of OFDM which has emerged as a new keytechnology to improve efficiency in advanced infrastructure-basedwireless networks. It combines OFDM on the physical layer with FrequencyDivision Multiple Access (FDMA) on the MAC layer, allowing differentsub-carriers or tones to be assigned to different nodes in order toincrease concurrency. Adjacent sub-carriers often experience similarchannel conditions and are thus grouped to sub-channels: an OFDMAsub-channel or RU is thus a set of sub-carriers or tones.

As currently envisaged, the granularity of such OFDMA sub-channels isfiner than the original 20 MHz channel band. Typically, a 2 MHz or 5 MHzsub-channel may be contemplated as a minimal width, therefore definingfor instance nine sub-channels or resource units within a single 20 MHzchannel.

To support multi-user uplink, i.e. uplink transmission to the 802.11axaccess point (AP) during the granted TxOP, the 802.11ax AP has toprovide signalling information for the legacy nodes (non-802.11ax nodes)to set their NAV and for the 802.11ax nodes to determine the allocationof the resource units RUs, and to be used as a reference time for thesynchronization of the data emission.

It has been proposed for the AP to send a trigger frame (TF) to the802.11ax nodes to trigger uplink communications.

The document IEEE 802.11-15/0365 proposes that a ‘Trigger’ frame (TF) issent by the AP to solicit the transmission of uplink (UL) Multi-User(OFDMA) PPDU from multiple nodes. In response, the nodes transmit UL MU(OFDMA) PPDU as immediate responses to the Trigger frame. Alltransmitters can send data at the same time, but using disjoint sets ofRUs (i.e. of frequencies in the OFDMA scheme), resulting intransmissions with less interference.

OFDMA to provide multi-user transmission in 802.11ax requires accurateinter-user symbol synchronization to keep the orthogonality among thedifferent OFDMA sub-channels or RUs.

In addition, the various nodes transmitting PPDUs on the RUs have tosynchronize the end of their PPDUs transmission, Otherwise, if a nodeends its transmission earlier, the unused RU could be acquired by anOBSS (Overlapping Base Station Subsystem) node, which may then initiatea new transmission.

This may cause interference with the following Block Acknowledgements(BAs) sent by the AP to the nodes.

This may also disturb the AP when receiving of the other on-going PPDUs.

To synchronize the end of their PPDUs transmission, the nodes must senddata on their RUs until the end of the TXOP time duration indicated inthe trigger frame. In practice, the nodes starts sending padding data(as defined in the document IEEE 802.11-15/617) if they end transmittingpayload data before the end of the TXOP.

The bandwidth or width of the targeted composite channel is alsosignalled in the TF frame, meaning that the 20, 40, 80 or 160 MHz valueis added. The TF frame is sent over the primary 20 MHz channel andduplicated (replicated) on each other 20 MHz channels forming thetargeted composite channel. As described above for the duplication ofcontrol frames, it is expected that every nearby legacy node (non-HT or802.11ac nodes) receiving the TF on its primary channel, then sets itsNAV to the TXOP duration value specified in the TF frame. This preventsthese legacy nodes from accessing the channels of the targeted compositechannel during the TXOP.

A resource unit RU can be reserved for a specific node, in which casethe AP indicates, in the TF, the node to which the RU is reserved. SuchRU is called Scheduled RU. The indicated node does not need to performcontention on accessing a scheduled RU reserved to it.

In order to better improve the efficiency of the system in regards tounmanaged traffic to the AP (for example, uplink management frames fromassociated nodes, non-associated nodes intending to reach an AP, orsimply unmanaged data traffic), the document IEEE 802.11-15/0604proposes a new trigger frame (TF-R) above the previous UL MU procedure,allowing random access onto the OFDMA TXOP. In other words, the resourceunit RU can be randomly accessed by more than one node. Such RU iscalled Random RU and is indicated as such in the TF. Random RUs mayserve as a basis for contention between nodes willing to access thecommunication medium for sending data.

The random resource selection procedure is not yet defined. All that isknown is that the trigger frame may define only Scheduled RUs, or onlyRandom RUs within the targeted composite channel.

Whatever the random resource selection procedure used, multi-usertransmission based on the Trigger Frame mechanism should improve networkcapacity by mutualizing the overhead over the nodes. Indeed, waitingtime overhead is reduced on overall.

However, it is believed that the Trigger Frame mechanism still suffersfrom overhead issue, mainly moved from waiting time to padding time.

To be precise, the Trigger Frame mechanism provides only generic RU inwhich padding must be performed to ensure reaching the end of the TXOPand to avoid interference with legacy nodes. Such padding adds to theoverall cost of overhead. This additional overhead cost due to paddingis exacerbated for the so-called small packets, since they use a verylittle portion of allocated RUs.

So, particularly for small packets, the gain in reducing the waitingtime may not be enough to compensate the loss due to padding. As aresult, the total overhead may not be reduced, contrary to the intendedgoal when introducing the Trigger Frame mechanism.

Apart from the small packet situation, different kinds of data trafficusually cohabit in the various RUs, each with different requirements interm of data quantity to transmit, latency. TxOP duration, etc. Suchheterogeneity of the different PPDUs transmitted by the nodes may resultin having a huge quantity of padding data in some RUs, and hence indrastically reducing the efficiency of the channel usage.

It may be noted that the padding issue may also be accentuated by theuse of different modulations (Modulation and Coding Scheme) to handlethe distance (node to AP) and Signal Noise Ratio variation (channelconditions change) through the different paths, i.e. through thedifferent RUs involving different nodes.

Thus, there is a need to improve this situation and to reduce the impactof padding in network usage efficiency.

In addition, it may also be taken advantage of the different kinds ofdata traffic cohabiting in the various RUs to improve the usage of thenetwork.

SUMMARY OF INVENTION

It is a broad objective of the present invention to provide wirelesscommunication methods and devices in a wireless network. The wirelessnetwork includes an access point and a plurality of nodes, all of themsharing the physical medium of the wireless network.

The present invention has been devised to overcome one or more foregoinglimitations.

In this context, the present invention seeks to provide wirelesscommunication methods improving usage of the network and, in turns,having improved mechanisms against collisions in communication channels.

The invention can be applied to any wireless network in which an accesspoint provides the registered nodes with a plurality of sub-channels (orresource units) forming a communication channel. The communicationchannel is the elementary channel on which the nodes perform sensing todetermine whether it is idle or busy.

The invention is especially suitable for data transmission to the AP ofan IEEE 802.11ax network (and future version).

First main embodiments of the invention provide, from the access point'sperspective, a wireless communication method in a wireless networkcomprising an access point and a plurality of nodes, the methodcomprising, at the access point, the step of sending a trigger frame tothe nodes, the trigger frame reserving at least one communicationchannel of the wireless network for a transmission opportunity anddefining a plurality of resource units forming the communicationchannel,

wherein the trigger frame includes an indicator restricting data to besent on at least one of the resource units to data having a restrictedtype of data.

The same first main embodiments of the invention provide, from thenode's perspective, a wireless communication method in a wirelessnetwork comprising an access point and a plurality of nodes, the methodcomprising, at one of said nodes:

receiving a trigger frame from the access point, the trigger framereserving at least one communication channel of the wireless network fora transmission opportunity and defining a plurality of resource unitsforming the communication channel;

determining, from the trigger frame, an indicator defining a restrictedtype of data authorized for at least one of the resource units:

determining, from local transmitting memory, data having a typecorresponding to the determined restricted type of data; and

transmitting the determined data to the access point on the saidresource unit.

Thanks to the indicator specifying the restricted type of data, theAccess Point is able to drive or control the nodes in their process ofselecting data to transmit on the RUs. As a consequence, the AP mayefficiently adapt the RUs to data types, resulting in optimizing the useof the RUs.

Correlatively, the invention provides a communication device acting asan access point in a wireless network also comprising a plurality ofnodes, the communication device acting as an access point comprising atleast one microprocessor configured for carrying out the step of sendinga trigger frame to the nodes, the trigger frame reserving at least onecommunication channel of the wireless network for a transmissionopportunity and defining a plurality of resource units forming thecommunication channel,

wherein the trigger frame includes an indicator restricting data to besent on at least one of the resource units to data having a restrictedtype of data.

From the node's perspective, the invention also provides a communicationdevice in a wireless network comprising an access point and a pluralityof nodes, the communication device being one of the nodes and comprisingat least one microprocessor configured for carrying out the steps of:

receiving a trigger frame from the access point, the trigger framereserving at least one communication channel of the wireless network fora transmission opportunity and defining a plurality of resource unitsforming the communication channel;

determining, from the trigger frame, an indicator defining a restrictedtype of data authorized for at least one of the resource units;

determining, from local transmitting memory, data having a typecorresponding to the determined restricted type of data; and

transmitting the determined data to the access point on the saidresource unit.

Optional features of embodiments of the invention are defined in theappended claims. Some of these features are explained here below withreference to a method, while they can be transposed into system featuresdedicated to any node device according to embodiments of the invention.

In embodiments, the restricted type of data defines small MAC packetsrelative to the MAC packets conveyed over the wireless network. As aconsequence, the AP may force the nodes to transmit their so-calledsmall packets. As a consequence, the nodes will less often spend time toobtain TXOP for sending small packets. This greatly contributes toreduce the overall overhead costs due to small packets. As aconsequence, network usage is improved.

In specific embodiments, small MAC packets are MAC packets having apacket size lower than a predetermined maximum small packet size (i.e.threshold). For instance, the predefined maximum small packet sizeequals a so-called RTS Threshold parameter set for the wireless networkaccording to the 802.11 standard. It is known that the RTS Thresholdparameter is a manageable parameter of 802.11 network used to determinewhen (i.e. from which size of MAC packets) an RTS/CTS handshake shouldprecede a data packet.

As a consequence, the small packets that are usually handled withoutRTS/CTS handshake (i.e. for which overhead due to RTS/CTS should beavoided) are processed in bursts using the TF.

In variants, small MAC packets are MAC packets having an overhead due toa MAC header in the packets that is higher than a predetermined maximumoverhead (i.e. threshold), for instance 20% or 30%. Indeed, thosepackets having already a big internal overhead should preferably behandled together by bursts in order to avoid having too much additionaloverhead per packet.

There are some types of packets that intrinsically have one or the otherdefinition above. For instance, control packets are by nature smallpackets.

In specific embodiments, the predetermined maximum small packet size ormaximum overhead is specified in the trigger frame.

In embodiments from the access point's perspective, the method mayfurther comprise adjusting the predetermined maximum small packet sizeor maximum overhead from one trigger frame to the other, based onnetwork statistics on one or more previous transmission opportunities.

These two provisions make it possible for the AP to efficiently drivethe management of the small packets, as the network conditions evolve.

In embodiments from the node's perspective, the node's localtransmitting memory includes a plurality of ordered transmitting queues,each being associated with a dynamic priority value (i.e. the priorityvalue evolves over time. In 802.11 scheme, the priority valuecorresponds to the value of a contention backoff counter associated witheach transmitting queue); and

determining data having a type corresponding to the determinedrestricted type of data comprises selecting at least one small packetfrom a set of one or more small packets, the set being made of one from:

the first small packet from the transmitting queue having the highestpriority value,

the first small packet from each transmitting queue,

all the small packets from all the transmitting queue,

all the packets of a transmitting queue storing only small packets.

Strategy on the nodes may thus be adapted.

In embodiments, the said one resource unit has minimal frequency widthauthorized by the 802.11 standard. Currently, the 20 MHz channel can besplit into a maximum of nine identical resource units, i.e. with aminimal frequency width of 2.03 MHz. This provision optimizes the use ofthe RUs to small packets. As a result, it also increases the number ofnodes that can send small packets on the RUs of the granted compositechannel.

In embodiments, the restricted type of data defines a traffic type ofdata. As a consequence, the AP may force the nodes to transmit somekinds of data in response to specific TF. As it will transpires frombelow, the AP will then adapt the RUs according to the traffic typesallowed, in order to optimize usage of the network bandwidth.

In specific embodiments, the restricted traffic type of data is one ofthe four access categories defined in the 802.11 standard, namely AC_BKfor background data, AC_BE for best-effort data, AC_VI for videoapplications and AC_VO for voice applications.

In specific embodiments from the AP's perspective, the method furthercomprises determining the restricted traffic type of data from aplurality of predefined traffic types (for instance the four accesscategories above), based on:

either network statistics on the amount of data received in one or moreprevious transmission opportunities for each of the predefined traffictypes,

or a total queue size for each of the predefined traffic types, a totalqueue size for a predefined traffic type summing the sizes oftransmission queues that are associated, in the nodes, with thepredefined traffic type. The AP may obtain such information from eachnode because the 802.11 standard MAC header of the PPDUs sent by thenodes includes a “Queue Size” field through which the nodes indicate theamount of their buffered traffic for a given traffic type. So the AP isable to compute global statistics on the total queue size for eachtraffic type and to build an associated trigger frame with dedicated RUtraffic type.

In specific embodiments from the node's perspective, determining, fromlocal transmitting memory, data having a type corresponding to thedetermined restricted type of data includes selecting data in atransmitting queue storing data having only the determined restrictedtype of data. This particularly applies to the case where the restrictedtype of data is one of the four access categories defined above. In thatcase, processing at the node is very simple since it only has to accessa single transmitting queue, depending on the restricted type of dataassociated with the RU used.

In specific embodiments from the node's perspective, the node's localtransmitting memory includes a plurality of transmitting queues, eachbeing associated with a dynamic priority value and with a traffic type,and the method further comprises:

successively considering the transmitting queue according to anhighest-to-lowest priority value order, until data is sent on a resourceunit,

and for each transmitting queue successively considered, determiningwhether a resource unit in the communication channel has the restrictedtraffic type, and in case of positive determination, transmitting datafrom the transmitting queue currently considered on the determinedresource unit.

This configuration keeps the priority order as defined in 802.11standard, thus keeping fairness between the nodes.

In embodiments, the method further comprises determining a frequency ofsending a trigger frame having a restricted type indicator, based onnetwork statistics on one or more previous transmission opportunities.This contributes to improve network usage since the AP dynamicallyadapts the number of opportunities for the nodes to transmit specificdata (small packets or having traffic types) to the network conditions.

In other embodiments, the method further comprises determining thenumber of resource units forming the communication channel, based onnetwork statistics on one or more previous transmission opportunities.This contributes to improve network usage since the number of nodes thatcan transmit data during the next TXOP is dynamically adjusted to thenetwork conditions.

In specific embodiments, the network statistics include one or morefrom:

a number of nodes registered to the access point in the wirelessnetwork,

a number of collisions or a collision ratio (number of colliding RUs outof the number of RUs) occurring during the one or more previoustransmission opportunities,

a distribution of packet sizes received by the access point, inparticular a packet size distribution relative to a maximum packet size(i.e. defining the small packets),

an amount of data transmitted by the nodes,

an amount of data transmitted by the nodes for each traffic type fromamong a plurality of predefined traffic types,

a ratio of medium busyness, for instance the ratio of a medium busy timeon a given period (e.g. one second).

In embodiments, the trigger frame includes a single indicator thatdefine the same restricted type of data for all the resource units ofthe at least one communication channel, i.e. for the whole compositechannel. Overhead due to the indicator is thus minimized.

In variants, the trigger frame includes one indicator per resource unit,thus defining various restricted types of data for various respectiveresource units. This is to allow more nodes to send data during thecurrent TXOP, since nodes having different types of data may now sendthrough respective RUs within the same communication channel.

Second main embodiments of the invention provide, from the accesspoint's perspective, a wireless communication method in a wirelessnetwork comprising an access point and a plurality of nodes, the methodcomprising, at the access point, the step of sending a trigger frame tothe nodes, the trigger frame reserving at least one communicationchannel of the wireless network for a transmission opportunity anddefining a plurality of resource units forming the communicationchannel, at least one resource unit having a predefined resource unitfrequency width,

wherein the method further comprises, at the access point, the step ofdetermining a duration of the transmission opportunity based on thepredefined resource unit frequency width and a predetermined maximumsmall packet size, so that the at least one resource unit can onlyinclude MAC packets having a packet size lower than the predeterminedmaximum small packet size.

This configuration makes it possible for the access point to force thenodes to transmit their so-called small packets (i.e. having a packetsize lower than a predetermined maximum packet size). This is achievedby sizing the TXOP in an appropriate manner given the predefined widthof the resource unit.

One advantage of using this approach to force transmission of smallpackets is that it is fully compliant with 802.11ax standard. Indeed, noaddition information is provided, and the nodes still perform the sameprocess to select data matching the RU offers.

Correlatively, the invention provides a communication device acting asan access point in a wireless network also comprising a plurality ofnodes, the communication device acting as an access point comprising atleast one microprocessor configured for carrying out the step of sendinga trigger frame to the nodes, the trigger frame reserving at least onecommunication channel of the wireless network for a transmissionopportunity and defining a plurality of resource units forming thecommunication channel, at least one resource unit having a predefinedresource unit frequency width,

wherein the microprocessor is further configured for carrying out thestep of determining a duration of the transmission opportunity based onthe predefined resource unit frequency width and a predetermined maximumsmall packet size, so that the at least one resource unit can onlyinclude MAC packets having a packet size lower than the predeterminedmaximum small packet size.

Optional features of embodiments of the invention are defined in theappended claims. Some of these features are explained here below withreference to a method, while they can be transposed into system featuresdedicated to any node device according to embodiments of the invention.

In embodiments, the predefined maximum small packet size equals aso-called RTS Threshold parameter set for the wireless network accordingto the 802.11 standard.

In embodiments, the predefined resource unit width is a minimalfrequency width authorized by the 802.11 standard.

A frequency for sending such a trigger frame or the number of resourceunits in the communication channel may also be determined dynamically asexplained above with reference to the first main embodiments.

Third main embodiments of the invention provide, from the access point'sperspective, a wireless communication method in a wireless networkcomprising an access point and a plurality of nodes, the methodcomprising, at the access point, the step of:

sending a trigger frame to the nodes, the trigger frame reserving atleast one communication channel of the wireless network for atransmission opportunity and defining a plurality of resource unitsforming the communication channel, the plurality of resource unitshaving the same time length;

wherein resource units within the communication channel have differentfrequency widths.

The same third main embodiments of the invention provide, from thenode's perspective, a wireless communication method in a wirelessnetwork comprising an access point and a plurality of nodes, the methodcomprising, at one of said nodes, the steps of:

receiving a trigger frame from the access point, the trigger framereserving at least one communication channel of the wireless network fora transmission opportunity and a plurality of resource units forming thecommunication channel, the plurality of resource units having the sametime length, and

transmitting data to the access point on one of the resource units,

wherein resource units within the communication channel have differentfrequency widths.

Use of network bandwidth is optimized. This is achieved by havingresource units with different frequency widths, i.e. with differenttransmission capacities.

As a consequence, the nodes may efficiently select resource unitsmatching their needs, in order to minimize the padding.

Correlatively, the invention provides a communication device acting asan access point in a wireless network also comprising a plurality ofnodes, the communication device acting as an access point comprising atleast one microprocessor configured for carrying out the step of sendinga trigger frame to the nodes, the trigger frame reserving at least onecommunication channel of the wireless network for a transmissionopportunity and defining a plurality of resource units forming thecommunication channel, the plurality of resource units having the sametime length;

wherein resource units within the communication channel have differentfrequency widths.

From the node's perspective, the invention also provides a communicationdevice in a wireless network comprising an access point and a pluralityof nodes, the communication device being one of the nodes and comprisingat least one microprocessor configured for carrying out the steps of:

receiving a trigger frame from the access point, the trigger framereserving at least one communication channel of the wireless network fora transmission opportunity and a plurality of resource units forming thecommunication channel, the plurality of resource units having the sametime length, and

transmitting data to the access point on one of the resource units,

wherein resource units within the communication channel have differentfrequency widths.

Optional features of embodiments of the invention are defined in theappended claims. Some of these features are explained here below withreference to a method, while they can be transposed into system featuresdedicated to any node device according to embodiments of the invention.

In embodiments, each resource unit is associated with a traffic type ofdata selected from the four access categories defined in the 802.11standard, namely AC_BK for background data, AC_BE for best-effort data,AC_VI for video applications and AC_VO for voice applications.

In specific embodiments, the resource unit or units associated withAC_BK and AC_BE traffic type have a first frequency width, the resourceunit or units associated with AC_VO have a frequency width equal totwice the first frequency width and the resource unit or unitsassociated with AC_VI have a frequency width equal to four times thefirst frequency width. This provision optimizes usage of the bandwidthsince the RU sizes are adapted to the size of the content they convey.As a result the resource units dedicated to small contents are sizedaccordingly in order to avoid too many padding.

In more specific embodiments, the first frequency width equals a minimalfrequency width authorized by the 802.11 standard. Currently, the 20 MHzchannel is split into a maximum of nine identical resource units, i.e.the minimal frequency width is 2.03 MHz. This is to offer the bestgranularity for the access point when designing the resource units.

In specific embodiments, the same time length of the resource units isless or equal to a quarter of a TXOP Limit parameter set for thewireless network according to the 802.11 standard. This provision isadvantageously combined with the above relative sizing (width) of theresource units depending on their associated AC_BK, AC_BE, AC_VI orAC_VO traffic types. Indeed, playing on the RU width makes it possibleto substantially reduce the duration of the TXOP, and thus the paddingfor the under-used RUs.

In embodiments relating to the nodes, each resource unit is associatedwith a traffic type of data, and the method further comprises, at thenode:

transmitting, on one resource unit, data having the same traffic type asthe traffic type associated with the resource unit.

This helps the access point to drive the way the nodes use the resourceunits. The access node may define the traffic type for each resourceunit in the trigger frame.

In embodiments, the node includes a plurality of transmitting queuesstoring data to be sent, each being associated with a dynamic priorityvalue; and the method further comprises:

determining whether one of the resource units matches the amount of datato be sent in the transmitting queue having the highest priority value,and

in case of positive determining, transmitting the data of thetransmitting queue having the highest priority value on the matchingresource unit.

Of course, the other transmitting queues may be successively consideredaccording to the priority order, in order to transmit their content inappropriate (i.e. well-sized) RUs.

In embodiments, the method further comprises adapting a modulationscheme for modulating the data on the resource unit, the adaptingmaximizing the time duration of transmitting the data within thetransmission opportunity. This also contributes to reduce the padding inthe RUs, while strengthening the data against errors occurring on thecommunication channel.

In embodiments relating to the access point, each resource unit isassociated with a traffic type of data, and the method furthercomprises:

determining the frequency widths of the resource units based onstatistics on data related to each traffic type as received in one ormore previous transmission opportunities.

This is for the access point to dynamically adjust the RU design to thenode needs, i.e. as the network conditions evolve.

In specific embodiments, the frequency widths of the resource units arefurther adjusted based on the number of nodes registered to the accesspoint. This provision also helps adjusting the number of RUs based onthe number of nodes, since the frequency widths of the RUs may beadjusted to make it possible to add or remove one or more RUs in thecommunication channel.

In specific embodiments, the frequency width of a resource unitassociated with a traffic type is further adjusted based on a modulationscheme used by the nodes to send data having the associated traffic typein one or more previous transmission opportunities. This provision helpsreducing padding in the RUs when the transmission of useful data ends,while strengthening the robustness of the transmitted data againsttransmission errors.

In embodiments, the method further comprises determining the number ofresource units forming the communication channel, based on networkstatistics on one or more previous transmission opportunities.

The same statistics as defined above may be used. In particular, thetype of data traffic (video, voice, background, best effort), thequantity of each data traffic type, the number of nodes, the modulationscheme (MCS) used by each node, the modulation scheme (MCS) used on eachRU, the identification of steady traffic (video streaming, VoIP . . . )or random traffic (Web browsing, control frame . . . ), may be used.

Another aspect of the invention relates to a non-transitorycomputer-readable medium storing a program which, when executed by amicroprocessor or computer system in a device of a wireless network,causes the device to perform any method as defined above.

The non-transitory computer-readable medium may have features andadvantages that are analogous to those set out above and below inrelation to the methods and node devices.

Another aspect of the invention relates to a wireless communicationmethod in a wireless network comprising an access point and a pluralityof nodes, substantially as herein described with reference to, and asshown in, FIG. 8 or FIG. 9 or FIG. 10 or FIG. 11 or FIG. 12 or FIG. 13of the accompanying drawings.

At least parts of the methods according to the invention may be computerimplemented. Accordingly, the present invention may take the form of anentirely hardware embodiment, an entirely software embodiment (includingfirmware, resident software, micro-code, etc.) or an embodimentcombining software and hardware aspects that may all generally bereferred to herein as a “circuit”, “module” or “system”. Furthermore,the present invention may take the form of a computer program productembodied in any tangible medium of expression having computer usableprogram code embodied in the medium.

Since the present invention can be implemented in software, the presentinvention can be embodied as computer readable code for provision to aprogrammable apparatus on any suitable carrier medium. A tangiblecarrier medium may comprise a storage medium such as a hard disk drive,a magnetic tape device or a solid state memory device and the like. Atransient carrier medium may include a signal such as an electricalsignal, an electronic signal, an optical signal, an acoustic signal, amagnetic signal or an electromagnetic signal, e.g. a microwave or RFsignal.

BRIEF DESCRIPTION OF THE DRAWINGS

Further advantages of the present invention will become apparent tothose skilled in the art upon examination of the drawings and detaileddescription. Embodiments of the invention will now be described, by wayof example only, and with reference to the following drawings.

FIG. 1 illustrates a typical wireless communication system in whichembodiments of the invention may be implemented;

FIG. 2 is a timeline schematically illustrating a conventionalcommunication mechanism according to the IEEE 802.11 standard;

FIG. 3 illustrates 802.11ac channel allocation that support channelbandwidth of 20 MHz, 40 MHz, 80 MHz or 160 MHz as known in the art;

FIG. 4 illustrates an example of 802.11ax uplink OFDMA transmissionscheme, wherein the AP issues a Trigger Frame for reserving atransmission opportunity of OFDMA sub-channels (resource units) on an 80MHz channel as known in the art;

FIG. 5 illustrates exemplary communication lines according to anexemplary random allocation;

FIG. 5a illustrates an example of use of eight RUs forming a compositechannel;

FIG. 6 shows a schematic representation a communication device orstation in accordance with embodiments of the present invention;

FIG. 7 shows a schematic representation of a wireless communicationdevice in accordance with embodiments of the present invention;

FIG. 8 illustrates, using a flowchart, general steps of firstembodiments of the present invention, from an access point'sperspective;

FIG. 9 illustrates, using a flowchart, general steps of the firstembodiments of the present invention, from a node's perspective;

FIG. 10 illustrates, using a flowchart, general steps of secondembodiments of the present invention, from an access point'sperspective;

FIG. 11 illustrates, using a flowchart, general steps of the secondembodiments of the present invention, from a node's perspective;

FIG. 12 illustrates, using a flowchart, general steps of thirdembodiments of the present invention, from an access point'sperspective;

FIG. 13 illustrates, using a flowchart, general steps of the thirdembodiments of the present invention, from a node's perspective;

FIG. 14 illustrates an example of designing RUs of a composite channelaccording to the third embodiments; and

FIG. 15 presents an exemplary format for signalling RU attributesaccording to the first, second and third embodiments of the presentinvention.

DETAILED DESCRIPTION

The invention will now be described by means of specific non-limitingexemplary embodiments and by reference to the figures.

FIG. 1 illustrates a communication system in which several communicationnodes (or stations) 101-107 exchange data frames over a radiotransmission channel 100 of a wireless local area network (WLAN), underthe management of a central station, or access point (AP) 110. The radiotransmission channel 100 is defined by an operating frequency bandconstituted by a single channel or a plurality of channels forming acomposite channel.

Access to the shared radio medium to send data frames is based on theCSMA/CA technique, for sensing the carrier and avoiding collision byseparating concurrent transmissions in space and time.

Carrier sensing in CSMA/CA is performed by both physical and virtualmechanisms. Virtual carrier sensing is achieved by transmitting controlframes to reserve the medium prior to transmission of data frames.

Next, a source node first attempts through the physical mechanism, tosense a medium that has been idle for at least one DIFS (standing forDCF InterFrame Spacing) time period, before transmitting data frames.

However, if it is sensed that the shared radio medium is busy during theDIFS period, the source node continues to wait until the radio mediumbecomes idle. To do so, it starts a countdown backoff counter designedto expire after a number of timeslots, chosen randomly between [0, CW],CW (integer) being referred to as the Contention Window. This backoffmechanism or procedure is the basis of the collision avoidance mechanismthat defers the transmission time for a random interval, thus reducingthe probability of collisions on the shared channel. After the backofftime period, the source node may send data or control frames if themedium is idle.

One problem of wireless data communications is that it is not possiblefor the source node to listen while sending, thus preventing the sourcenode from detecting data corruption due to channel fading orinterference or collision phenomena. A source node remains unaware ofthe corruption of the data frames sent and continues to transmit theframes unnecessarily, thus wasting access time.

The Collision Avoidance mechanism of CSMA/CA thus provides positiveacknowledgement (ACK) of the sent data frames by the receiving node ifthe frames are received with success, to notify the source node that nocorruption of the sent data frames occurred.

The ACK is transmitted at the end of reception of the data frame,immediately after a period of time called Short InterFrame Space (SIFS).

If the source node does not receive the ACK within a specified ACKtimeout or detects the transmission of a different frame on the channel,it may infer data frame loss. In that case, it generally reschedules theframe transmission according to the above-mentioned backoff procedure.However, this can be seen as a bandwidth waste if only the ACK has beencorrupted but the data frames were correctly received by the receivingnode.

To improve the Collision Avoidance efficiency of CSMA/CA, a four-wayhandshaking mechanism is optionally implemented. One implementation isknown as the RTS/CTS exchange, defined in the 802.11 standard.

The RTS/CTS exchange consists in exchanging control frames to reservethe radio medium prior to transmitting data frames during a transmissionopportunity called TXOP in the 802.11 standard as described below, thusprotecting data transmissions from any further collisions.

FIG. 2 illustrates the behaviour of three groups of nodes during aconventional communication over a 20 MHz channel of the 802.11 medium:transmitting or source node 20, receiving or addressee or destinationnode 21 and other nodes 22 not involved in the current communication.

Upon starting the backoff process 270 prior to transmitting data, astation e.g. source node 20, initializes its backoff time counter to arandom value as explained above. The backoff time counter is decrementedonce every time slot interval 260 for as long as the radio medium issensed idle (countdown starts from T0, 23 as shown in the Figure).

Channel sensing is for instance performed using Clear-Channel-Assessment(CCA) signal detection.

CCA is a WLAN carrier sense mechanisms defined in the IEEE 802.11-2007standards as part of the Physical Medium Dependant (PMD) and PhysicalLayer Convergence Protocol (PLOP) layer. It involves two functions:

Carrier Sense (CCA-CS) which is the ability of the receiving node todetect and decode an 802.11 frame preamble. From the PLOP header field,the time duration for which the medium will be occupied can be inferredand when such 802.11 frame preamble is detected, a CCA flag is held busyuntil the end of data transmission.

Energy Detect (CCA-ED) which is the ability of the receiving node todetect non-802.11 energy in a specific 20 MHz channel and back off datatransmission. In practice, a level of energy over the 20 MHz channel issensed and compared to an ED threshold discriminating between a channelstate with or without 802.11 energy channel. The ED threshold is forinstance defined to be 20 dB above the minimum sensitivity of a PHYlayer of the node. If the in-band signal energy crosses this threshold,CCA is held busy until the medium energy becomes below the thresholdanew.

The time unit in the 802.11 standard is the slot time called ‘aSlotTime’parameter. This parameter is specified by the PHY (physical) layer (forexample, aSlotTime is equal to 9 μs for the 802.11n standard). Alldedicated space durations (e.g. backoff) add multiples of this time unitto the SIFS value.

The backoff time counter is ‘frozen’ or suspended when a transmission isdetected on the radio medium channel (countdown is stopped at T1, 24 forother nodes 22 having their backoff time counter decremented).

The countdown of the backoff time counter is resumed or reactivated whenthe radio medium is sensed idle anew, after a DIFS time period. This isthe case for the other nodes at T2, 25 as soon as the transmissionopportunity TXOP granted to source node 20 ends and the DIFS period 28elapses. DIFS 28 (DCF inter-frame space) thus defines the minimumwaiting time for a source node before trying to transmit some data. Inpractice, DIFS=SIFS+2*aSlotTime.

When the backoff time counter reaches zero (26) at T1, the timerexpires, the corresponding node 20 requests access onto the medium inorder to be granted a TXOP, and the backoff time counter isreinitialized 29 using a new random backoff value.

In the example of the Figure implementing the RTS/CTS scheme, at T1, thesource node 20 that wants to transmit data frames 230 sends a specialshort frame or message acting as a medium access request to reserve theradio medium, instead of the data frames themselves, just after thechannel has been sensed idle for a DIFS or after the backoff period asexplained above.

The medium access request is known as a Request-To-Send (RTS) message orframe. The RTS frame generally includes the addresses of the source andreceiving nodes (“destination 21”) and the duration for which the radiomedium is to be reserved for transmitting the control frames (RTS/CTS)and the data frames 230.

Upon receiving the RTS frame and if the radio medium is sensed as beingidle, the receiving node 21 responds, after a SIFS time period 27 (forexample, SIFS is equal to 16 μs for the 802.11n standard), with a mediumaccess response, known as a Clear-To-Send (CTS) frame. The CTS framealso includes the addresses of the source and receiving nodes, andindicates the remaining time required for transmitting the data frames,computed from the time point at which the CTS frame starts to be sent.

The CTS frame is considered by the source node 20 as an acknowledgmentof its request to reserve the shared radio medium for a given timeduration.

Thus, the source node 20 expects to receive a CTS frame 220 from thereceiving node 21 before sending data 230 using unique and unicast (onesource address and one addressee or destination address) frames.

The source node 20 is thus allowed to send the data frames 230 uponcorrectly receiving the CTS frame 220 and after a new SIFS time period27.

To provide QoS support, 802.11 has defined various levels of prioritiesfor data the source node 20 wants to transmit. The levels are mainlydefined based on the nature of the data.

In 802.11e, four Access Categories (AC) are defined:

AC_BK has the lowest priority for background data,

AC_BE has the next priority for best-effort data,

AC_VI has higher priority for video applications, and

AC_VO has the highest priority for voice applications.

Each access category owns one or more traffic classes as defined in theIEEE standard 802.11e-2005.

In practice, the source node 20 has one transmitting buffer queue foreach access category and thus implements a backoff counter for eachaccess category. The backoff counter having the lowest value from amongthe four AC backoff counter is considered as being the backoff counterfor the node as discussed above, since it is the first one to reachzero.

An ACK frame 240 is sent by the receiving node 21 after having correctlyreceived the data frames sent, after a new SIFS time period 27.

If the source node 20 does not receive the ACK 240 within a specifiedACK Timeout (generally within the TXOP), or if it detects thetransmission of a different frame on the radio medium, it reschedulesthe frame transmission using the backoff procedure anew.

Since the RTS/CTS four-way handshaking mechanism 210/220 is optional inthe 802.11 standard, it is possible for the source node 20 to send dataframes 230 immediately upon its backoff time counter reaching zero (i.e.at T1).

The requested time duration for transmission defined in the RTS and CTSframes defines the length of the granted transmission opportunity TXOP,and can be read by any listening node (“other nodes 22” in FIG. 2) inthe radio network.

To do so, each node has in memory a data structure known as the networkallocation vector or NAV to store the time duration for which it isknown that the medium will remain busy. When listening to a controlframe (RTS 210 or CTS 220) not addressed to itself, a listening node 22updates its NAVs (NAV 255 associated with RTS and NAV 250 associatedwith CTS) with the requested transmission time duration specified in thecontrol frame. The listening nodes 22 thus keep in memory the timeduration for which the radio medium will remain busy.

Access to the radio medium for the other nodes 22 is consequentlydeferred 30 by suspending 31 their associated timer and then by laterresuming 32 the timer when the NAV has expired.

This prevents the listening nodes 22 from transmitting any data orcontrol frames during that period.

It is possible that receiving node 21 does not receive RTS frame 210correctly due to a message/frame collision or to fading. Even if it doesreceive it, receiving node 21 may not always respond with a CTS 220because, for example, its NAV is set (i.e. another node has alreadyreserved the medium). In any case, the source node 20 enters into a newbackoff procedure.

The RTS/CTS four-way handshaking mechanism is very efficient in terms ofsystem performance, in particular with regard to large frames since itreduces the length of the messages involved in the contention process.

In detail, assuming perfect channel sensing by each communication node,collision may only occur when two (or more) frames are transmittedwithin the same time slot after a DIFS 28 (DCF inter-frame space) orwhen their own back-off counter has reached zero nearly at the same timeT1. If both source nodes use the RTS/CTS mechanism, this collision canonly occur for the RTS frames. Fortunately, such collision is earlydetected by the source nodes since it is quickly determined that no CTSresponse has been received.

As described above, the original IEEE 802.11 MAC always sends anacknowledgement (ACK) frame 240 after each data frame 230 received.

However, such collisions limit the optimal functioning of the radionetwork. As described above, simultaneous transmission attempts fromvarious wireless nodes lead to collisions. The 802.11 backoff procedurewas first introduced for the DCF mode as the basic solution forcollision avoidance. In the emerging IEEE 802.11n/ac/ax standards, thebackoff procedure is still used as the fundamental approach forsupporting distributed access among mobile stations or nodes.

To meet the ever-increasing demand for faster wireless networks tosupport bandwidth-intensive applications, 802.11ac is targeting largerbandwidth transmission through multi-channel operations. FIG. 3illustrates 802.11ac channel allocation that support composite channelbandwidth of 20 MHz, 40 MHz, 80 MHz or 160 MHz

IEEE 802.11ac introduces support of a restricted number of predefinedsubsets of 20 MHz channels to form the sole predefined composite channelconfigurations that are available for reservation by any 802.11ac nodeon the wireless network to transmit data.

The predefined subsets are shown in the Figure and correspond to 20 MHz,40 MHz, 80 MHz, and 160 MHz channel bandwidths, compared to only 20 MHzand 40 MHz supported by 802.11n. Indeed, the 20 MHz component channels300-1 to 300-8 are concatenated to form wider communication compositechannels.

In the 802.11ac standard, the channels of each predefined 40 MHz, 80 MHzor 160 MHz subset are contiguous within the operating frequency band,i.e. no hole (missing channel) in the composite channel as ordered inthe operating frequency band is allowed.

The 160 MHz channel bandwidth is composed of two 80 MHz channels thatmay or may not be frequency contiguous. The 80 MHz and 40 MHz channelsare respectively composed of two frequency adjacent or contiguous 40 MHzand 20 MHz channels, respectively.

A node is granted a TxOP through the enhanced distributed channel access(EDCA) mechanism on the “primary channel” (300-3). Indeed, for eachcomposite channel having a bandwidth, 802.11ac designates one channel as“primary” meaning that it is used for contending for access to thecomposite channel. The primary 20 MHz channel is common to all nodes(STAs) belonging to the same basic set, i.e. managed by or registered tothe same local Access Point (AP).

However, to make sure that no other legacy node (i.e. not belonging tothe same set) uses the secondary channels, it is provided that thecontrol frames (e.g. RTS frame/CTS frame) reserving the compositechannel are duplicated over each 20 MHz channel of such compositechannel.

As addressed earlier, the IEEE 802.11ac standard enables up to four, oreven eight, 20 MHz channels to be bound. Because of the limited numberof channels (19 in the 5 GHz band in Europe), channel saturation becomesproblematic. Indeed, in densely populated areas, the 5 GHz band willsurely tend to saturate even with a 20 or 40 MHz bandwidth usage perWireless-LAN cell.

Developments in the 802.11ax standard seek to enhance efficiency andusage of the wireless channel for dense environments.

In this perspective, one may consider multi-user transmission features,allowing multiple simultaneous transmissions to different users in bothdownlink and uplink directions. In the uplink, multi-user transmissionscan be used to mitigate the collision probability by allowing multiplenodes to simultaneously transmit.

To actually perform such multi-user transmission, it has been proposedto split a granted 20 MHz channel (300-1 to 300-4) into sub-channels 410(elementary sub-channels), also referred to as sub-carriers or resourceunits (RUs), that are shared in the frequency domain by multiple users,based for instance on Orthogonal Frequency Division Multiple Access(OFDMA) technique. Each RU may be defined by a number of tones, the 20MHz channel containing up to 242 usable tones.

This multi-user transmission is illustrated with reference to FIG. 4.

The multi-user feature of OFDMA allows the AP to assign different RUs todifferent nodes in order to increase competition. This may help toreduce contention and collisions inside 802.11 networks.

Contrary to downlink OFDMA wherein the AP can directly send multipledata to multiple stations (supported by specific indications inside thePLCP header), a trigger mechanism has been adopted for the AP to triggeruplink communications from various nodes.

To support an uplink multi-user transmission (during a pre-empted TxOP),the 802.11ax AP has to provide signalling information for both legacystations (non-802.11ax nodes) to set their NAV and for 802.11ax nodes todetermine the Resource Units allocation.

In the following description, the term legacy refers to non-802.11axnodes, meaning 802.11 nodes of previous technologies that do not supportOFDMA communications.

As shown in the example of FIG. 4, the AP sends a trigger frame (TF) 430to the targeted 802.11ax nodes. The bandwidth or width of the targetedcomposite channel is signalled in the TF frame, meaning that the 20, 40,80 or 160 MHz value is added. The TF frame is sent over the primary 20MHz channel and duplicated (replicated) on each other 20 MHz channelsforming the targeted composite channel. As described above for theduplication of control frames, it is expected that every nearby legacynode (non-HT or 802.11ac nodes) receiving the TF on its primary channel,then sets its NAV to the value specified in the TF frame in order. Thisprevents these legacy nodes from accessing the channels of the targetedcomposite channel during the TXOP.

The trigger frame TF may designate at least one resource unit (RU) 410,or “Random RU”, which can be randomly accessed by more than one node. Inother words, Random RUs designated or allocated by the AP in the TF mayserve as basis for contention between nodes willing to access thecommunication medium for sending data. An exemplary embodiment of suchrandom allocation is illustrated by FIG. 5.

The trigger frame TF may also designate Scheduled resource units, inaddition or in replacement of the Random RUs. Scheduled RUs may bereserved for certain nodes in which case no contention for accessingsuch RUs is needed.

In this context, the TF includes information specifying the type(Scheduled or Random) of the RUs. For instance, a tag may be used toindicate that all the RUs defined in the TF are Scheduled (tag=1) orRandom (tag=0). In case, Random RUs and Scheduled RUs are mixed withinthe TF, a bitmap (or any other equivalent information) may be used todefine the type of each RU (the bitmap may follow a known order of theRUs throughout the communication channels).

The multi-user feature of OFDMA allows the AP to assign different RUs todifferent nodes in order to increase competition. This may help toreduce contention and collisions inside 802.11 networks.

In the example of FIG. 4, each 20 MHz channel is sub-divided infrequency domain in four sub-channels or RUs 410, typically of size 5Mhz. These sub-channels (or resource units) are also referred to as“sub-carriers” or “traffic channels”.

Of course the number of RUs splitting a 20 MHz may be different fromfour. For instance, between two to nine RUs may be provided (thus eachhaving a size between 10 MHz and about 2.2 MHz).

As shown in the Figure, all the RUs 410 have the same time length 230(corresponding to the length of the TXOP).

FIG. 5 illustrates exemplary communication lines according to anexemplary random allocation procedure 500 that may be used by the nodesto access the Random RUs indicated in the TF. This random allocationprocedure is based on the reuse of the backoff counter values of thenodes for assigning an RU to a node of the network to send data.

An AP sends a trigger frame TF defining RUs with random access. In theexample of the Figure, eight RUs with the same bandwidth are defined fora 40 MHz composite channel, and the TF 430 is duplicated on the two 20MHz channels forming the composite channel. In other words, the networkis configured to handle four OFDMA Resource Units per each 20 MHzchannel.

Each node STA1 to STAn is a transmitting node with regards to receivingAP, and as a consequence, each node has at least one active backoffvalue (corresponding to the AC backoff counter having the lowest value).

The random allocation procedure comprises, for a node of a plurality ofnodes having an active backoff 510, a first step of determining from thetrigger frame the sub-channels or RUs of the communication mediumavailable for contention, a second step of verifying if the value of theactive backoff local to the considered node is not greater than thenumber of detected-as-available RUs, and then a step of sending data isperformed on the RU whom number equals the backoff value.

In other words, the Random RUs may be indexed in the TF, and each nodeuses the RUs having an index equal to the backoff value of the node.

As shown in the Figure, some Resource Units may not be used, forinstance RUs indexed 2 (410-2), 5, 7 and 8. This is due to therandomization process, and in the present example, due to the fact thatnone of the nodes has a backoff value equal to 2, 5, 7 or 8 when the TFis sent.

FIG. 5a illustrates an example of use of eight RUs forming the compositechannel (of course the number of OFDMA RUs may vary). The eight RUs havea similar design, i.e. the same time length (corresponding to the TXOPduration) and the same frequency width.

The AP sends a TF with the duration 550 for instance 3 ms and a numberof Random RUs and/or Scheduled RUs.

Upon receiving the TF, the nodes access the Scheduled RUs or contend foraccess (e.g. as described above with reference to FIG. 5) to the RandomRUs, and then transmit their data in the accessed RU or RUs during atime corresponding to the TXOP duration 900.

In this example, the data traffics sent by the nodes are heterogeneous,i.e. video, voice, web application, control frames, etc. are mixedwithin the same UpLink (UL) MultiUser (MU) OFDMA transmission.

As shown in the Figure, the resulting PPDUs are very different one fromthe other in term of duration.

This is because the amount of data to be transmitted greatly varies fromone data type to the other.

This is also because, even for the same type of data traffic or for thesame quantity of data to transmit, the modulation used by the nodes (themodulation is linked to the distance between the transmitting node andthe Access Point) substantially modifies the transmission duration.According to the modulation used (MCS0 to 9 in IEEE802.11ac), the numberof bit carried by each OFDM symbol changes, and for a given quantity ofdata, the transmission duration changes also knowing that the symbolduration is fixed.

For instance, node STA1 may transmit web browsing traffic (AC_BE: accesscategory best effort), node STA2 may transmit a control frame, and nodeSTA4 may transmit a large aggregation of video data frames (AC_VI:access category Video).

As shown in the Figure, the PPDU sent by STA4 (553) use the full TXOPduration of the UL MU OFDMA while the PPDU send by STA1 (551) requirespadding (552) to maintain a signal on the RU#1 for the entire TXOPduration. Indeed, if the data transmission lasts less than the TXOPduration 550, the nodes have to pad up (send padding data) up to the endof the UL MU transmission.

This example of FIG. 5a illustrates the drawbacks of the UL MUtransmission in some scenarios.

The so-called “small packets” as the one sent by STAT suffer fromimportant overhead, due to the important amount of padding required tohave a signal up to the end of TXOP 230. There is a need to mitigatethis situation and to improve efficiency of the Trigger Frame mechanismwhen small packets are transmitted.

Also, due to the heterogeneity of the different PPDUs transmitted by thenodes, a huge quantity of padding data is sent over the RUs. There is aneed to adapt the Trigger Frame mechanism to the heterogeneity of databetween the RUs.

All of these needs seek to improve usage of the network, in particularby reducing the padding.

Embodiments of the present invention find a particular application inenhancements of the 802.11ac standard, and more precisely in the contextof 802.11ax wherein dense wireless environments are more ascertained tosuffer from previous limitations.

Embodiments of the present invention provide improved wirelesscommunications with more efficient use of bandwidth while limiting therisks of collision. In particular, it is sought to reduce the amount ofpadding data.

An exemplary wireless network is an IEEE 802.11ac network (and upperversions). However, the invention applies to any wireless networkcomprising an access point AP 110 and a plurality of nodes 101-107transmitting data to the AP through a multi-user transmission. Theinvention is especially suitable for data transmission in an IEEE802.11ax network (and future versions) requiring better use ofbandwidth.

An exemplary management of multi-user transmission in such a network hasbeen described above with reference to FIGS. 1 to 5.

First main embodiments of the present invention provide that, inaddition to reserving at least one communication channel of the wirelessnetwork for a transmission opportunity and defining a plurality ofresource units forming the communication channel, the trigger frameincludes an indicator restricting data to be sent on at least one of theresource units to data having a restricted type of data.

As a consequence, the nodes may determine, from the trigger frame, anindicator defining a restricted type of data authorized for at least oneof the resource units; determine, from local transmitting memory, datahaving a type corresponding to the determined restricted type of data;and transmit the determined data to the access point on the saidresource unit.

By using such indicator, the AP may force the nodes to send specificdata that are particularly adapted to the design of the RUs.

Two main approaches are proposed for the first embodiments.

On one hand, the restricted type of data defines small MAC packetsrelative to the MAC packets conveyed over the wireless network. Thisapproach, described with more details below with reference to FIGS. 8and 9, is for the AP to control the transmission of so-called smallpackets, by sending appropriate trigger frames. Thus, depending on theamount of small packets in on-going communications (the AP is able toclassify the data conveyed over on-going communications), the AP maydecide to clean node's transmitting buffer with small packets, in orderto reduce overall contention time for the nodes and overall overhead dueto the small packets.

On the other hand, the restricted type of data defines a traffic type ofdata. Main embodiments refer, for the restricted traffic type of data,to one of the four access categories defined in the 802.11 standard,namely AC_BK for background data, AC_BE for best-effort data, AC_VI forvideo applications and AC_VO for voice applications. This approach isdescribed with more details below with reference to FIGS. 10 and 11. Asa consequence, the AP may force the nodes to use RUs with specifictraffic data, because it may consider the RUs forming the compositechannel are well designed for such specific type of data. Again,efficiently using the RUs makes that less padding data is sent. Thisimproves usage of the network bandwidth.

Other main embodiments of the invention provide that, in a trigger framereserving at least one communication channel of the wireless network fora transmission opportunity and defining a plurality of resource unitsforming the communication channel, the plurality of resource unitshaving the same time length, resource units within the communicationchannel are defined with different frequency widths.

The RUs provided in a composite channel are thus more adapted toheterogeneous data traffic. By selecting the RU to be used in anappropriate way (examples of selection procedure are described below),the nodes generally reduce the amount of padding sent. Usage of thenetwork bandwidth is thus improved.

For instance, the node may determine whether or not one of the resourceunits matches an amount of data to be sent in the priority ACtransmitting queue of the node, and in case of positive determining,transmitting the data of the priority AC transmitting queue on thematching resource unit.

The approach of these other main embodiments is described below withreference to FIGS. 12 to 14.

The main approaches of the first main embodiments and the approaches ofthe other main embodiments may be partly or entirely combined in orderto add their benefits in reducing the overall padding.

FIG. 6 schematically illustrates a communication device 600 of the radionetwork 100, configured to implement at least one embodiment of thepresent invention. The communication device 600 may preferably be adevice such as a microcomputer, a workstation or a light portabledevice. The communication device 600 comprises a communication bus 613to which there are preferably connected:

-   -   a central processing unit 611, such as a microprocessor, denoted        CPU;    -   a read only memory 607, denoted ROM, for storing computer        programs for implementing the invention;    -   a random access memory 612, denoted RAM, for storing the        executable code of methods according to embodiments of the        invention as well as the registers adapted to record variables        and parameters necessary for implementing methods according to        embodiments of the invention; and    -   at least one communication interface 602 connected to the radio        communication network 100 over which digital data packets or        frames or control frames are transmitted, for example a wireless        communication network according to the 802.11ac protocol. The        frames are written from a FIFO sending memory in RAM 612 to the        network interface for transmission or are read from the network        interface for reception and writing into a FIFO receiving memory        in RAM 612 under the control of a software application running        in the CPU 611.

Optionally, the communication device 600 may also include the followingcomponents:

-   -   a data storage means 604 such as a hard disk, for storing        computer programs for implementing methods according to one or        more embodiments of the invention;    -   a disk drive 605 for a disk 606, the disk drive being adapted to        read data from the disk 606 or to write data onto said disk;    -   a screen 609 for displaying decoded data and/or serving as a        graphical interface with the user, by means of a keyboard 610 or        any other pointing means.

The communication device 600 may be optionally connected to variousperipherals, such as for example a digital camera 608, each beingconnected to an input/output card (not shown) so as to supply data tothe communication device 600.

Preferably the communication bus provides communication andinteroperability between the various elements included in thecommunication device 600 or connected to it. The representation of thebus is not limiting and in particular the central processing unit isoperable to communicate instructions to any element of the communicationdevice 600 directly or by means of another element of the communicationdevice 600.

The disk 606 may optionally be replaced by any information medium suchas for example a compact disk (CD-ROM), rewritable or not, a ZIP disk, aUSB key or a memory card and, in general terms, by an informationstorage means that can be read by a microcomputer or by amicroprocessor, integrated or not into the apparatus, possibly removableand adapted to store one or more programs whose execution enables amethod according to the invention to be implemented.

The executable code may optionally be stored either in read only memory607, on the hard disk 604 or on a removable digital medium such as forexample a disk 606 as described previously. According to an optionalvariant, the executable code of the programs can be received by means ofthe communication network 603, via the interface 602, in order to bestored in one of the storage means of the communication device 600, suchas the hard disk 604, before being executed.

The central processing unit 611 is preferably adapted to control anddirect the execution of the instructions or portions of software code ofthe program or programs according to the invention, which instructionsare stored in one of the aforementioned storage means. On powering up,the program or programs that are stored in a non-volatile memory, forexample on the hard disk 604 or in the read only memory 607, aretransferred into the random access memory 612, which then contains theexecutable code of the program or programs, as well as registers forstoring the variables and parameters necessary for implementing theinvention.

In a preferred embodiment, the apparatus is a programmable apparatuswhich uses software to implement the invention. However, alternatively,the present invention may be implemented in hardware (for example, inthe form of an Application Specific Integrated Circuit or ASIC).

FIG. 7 is a block diagram schematically illustrating the architecture ofa communication device or node 600, either the AP 110 or one of nodes100-107, adapted to carry out, at least partially, the invention. Asillustrated, node 600 comprises a physical (PHY) layer block 703, a MAClayer block 702, and an application layer block 701.

The PHY layer block 703 (here an 802.11 standardized PHY layer) has thetask of formatting, modulating on or demodulating from any 20 MHzchannel or the composite channel, and thus sending or receiving framesover the radio medium used 100, such as 802.11 frames, for instancemedium access trigger frames TF 430 to reserve a transmission slot, MACdata and management frames based on a 20 MHz width to interact withlegacy 802.11 stations, as well as of MAC data frames of OFDMA typehaving smaller width than 20 MHz legacy (typically 2 or 5 MHz) to/fromthat radio medium.

The PHY layer block 703 includes CCA capability to sense the idle orbusy state of 20 Mhz channels and to report the result to the MAC 702according to 802.11 standard. Upon detecting a signal with significantreceived signal strength, an indication of channel use is generated.

The MAC layer block or controller 702 preferably comprises a MAC 802.11layer 704 implementing conventional 802.11ax MAC operations, and anadditional block 705 for carrying out, at least partially, theinvention. The MAC layer block 702 may optionally be implemented insoftware, which software is loaded into RAM 612 and executed by CPU 611.

Preferably, the additional block 705, referred to as the MU managementmodule, implements the parts dedicated to implement all or part of theembodiments of the invention that regards node 600.

For instance, when implementing the first approach of the first mainembodiments of the invention, an illustrating example of which beingdescribed below with reference to FIGS. 8 and 9, MU management module705 includes a small packet (SP) management module 7050, including a “TFHandler” sub-block 7051 for the AP to implement the algorithm of FIG. 8and/or a “RU selector” sub-block 7052 for each node to implement thealgorithm of FIG. 9.

When implementing the second approach of the first main embodiments ofthe invention, an illustrating example of which being described belowwith reference to FIGS. 10 and 11, MU management module 705 includes anaccess category (AC—or traffic type) management module 7052, which alsoincludes a “TF Handler” sub-block for the AP to implement one of thealgorithms of FIG. 10 and/or a “RU selector” sub-block for each node toimplement the algorithm of FIG. 11.

When implementing the other main embodiments of the invention, anillustrating example of which being described below with reference toFIGS. 12 to 14, MU management module 705 includes a frequency widthmanagement module 7053, which also includes a “TF Handler” sub-block forthe AP to implement the algorithm of FIG. 12 and/or a “RU selector”sub-block for each node to implement the algorithm of FIG. 14.

The exemplary node of FIG. 7 includes the features according to all theembodiments of the invention as described below with reference to FIGS.8 to 15.

On top of the Figure, application layer block 701 runs an applicationthat generates and receives data packets, for example data packets of avideo stream. Application layer block 701 represents all the stacklayers above MAC layer according to ISO standardization.

FIGS. 8 and 9 illustrate, using two flowcharts, general steps ofembodiments of the present invention which restrict data to be sent onat least one of the resource units to data having a restricted type ofdata, in particular to small MAC packets relative to the MAC packetsconveyed over the wireless network. FIG. 8 is a flowchart from theAccess Point's perspective, while FIG. 9 is a flowchart from the node'sperspective. They apply to multi-user OFDMA uplink in an 802.11axwireless medium.

Small packets may be defined in various ways.

First, small MAC packets may be MAC packets having a packet size lowerthan a predetermined maximum small packet size (i.e. threshold). Forinstance, the predefined maximum packet size equals a so-called RTSThreshold parameter set for the wireless network according to the 802.11standard. Typically, a value equal to 256 bit can be selected. Thethreshold size may be set in advance in the AP by the administrator orby default factory settings.

In a variant, the small packets may be defined relative to theiroverhead cost. For instance, small MAC packets may be MAC packets havingan overhead due to a MAC header in the packets that is higher than apredetermined maximum overhead (i.e. threshold). A typical ratio valueis 20% or 30%.

In a third embodiment, the threshold value (either the predeterminedmaximum small packet size or the predetermined maximum overhead) can bedynamically determined using a learning mechanism as described belowwith reference to step 804.

FIG. 8 illustrates an exemplary process for the AP to generate a TriggerFrame dedicated to collection of small packets (SP), also referred belowto as SP Trigger Frame or SP TF.

Such a SP trigger frame is built in order to force the nodes to sendonly small packets in specific RUs (preferably all the RUs or all theRandom RUs defined by the SP TF). To achieve that, the SP TF includes anindicator specifying such restriction to small packets.

Various implementations may be contemplated.

For instance, the restricting indicator specified in the SP TF may be apredetermined maximum small packet size or maximum overhead providing anupper bound when evaluating whether packets are small packets or not.Such information may be provided using a dedicated field 1522 in thesignaling shown in FIG. 15.

In variant, such upper bound may be predefined and known by all the APand nodes of the network. In such a case, there is only a need toindicate that the TF is SP TF either for all the RUs or for some RUs.

In embodiments, the restricting indicator defines a trigger frame type,namely the SP TF. It indicates that all the RUs defined by the SP TF arerestricted to small packets. In other words, the trigger frame includesa single indicator that define the same restricted type of data for allthe resource units of the at least one communication channel.

In other embodiments, the restriction may be defined at the RU level.That means that an indicator defined an RU traffic type: eitherrestricted to small packets, or not restricted. It means that thetrigger frame includes one indicator per resource unit, thus definingvarious restricted types of data for various respective resource units.For instance, a dedicated RU SP or traffic type field may be used in theRU description as described below with reference to FIG. 15, to limitthe usage of specific RUs to the transmission of small packets.

In a variant to the use of a specific restricting indicator in the SPTF, embodiments may provide that the duration of the TXOP is voluntarilymade very short in order to implicitly allow only small packets to betransmitted. To achieve this configuration, the AP shall determine aduration of the transmission opportunity based on a predefined resourceunit frequency width and a predetermined maximum small packet size, sothat the at least one resource unit can only include MAC packets havinga packet size lower than the predetermined maximum small packet size.Preferably, the predefined maximum small packet size equals theso-called RTS Threshold parameter set for the wireless network accordingto the 802.11 standard, and the predefined resource unit width is aminimal frequency width authorized by the 802.11 standard (2.2 MHz whena 20 MHz channel is split into nine RUs).

As described below, a scheduling of the SP TF sending is determined inorder to optimize the reduction of the small packet overhead. Thisincludes determining a frequency of sending a trigger frame having arestricted type indicator, based on network statistics on one or moreprevious transmission opportunities. It corresponds to the first steps800-803 of the process now described.

The process starts at step 799 where the AP determines if a new eventoccurs. If a new event occurs, step 799 determines whether the new eventcorresponds to the reception of a packet at MAC level, or corresponds tothe expiration of a SP TF timer as explained below, or corresponds toany other event.

When a packet is received at MAC level, next step 800 is executed duringwhich the AP (in a more general manner, any node in the network mayinitiate a TXOP by sending a TF, in which case FIG. 8 may be implementedby such a node) gathers some statistics about the wireless networkduring one or more previous TXOPs.

Exemplary statistics include the number of nodes in the network, thenumber or ratio of collisions (collided RUs), the number or ratio ofused RUs, the number or ratio of unused RUs, a distribution of thepacket size received by the AP, etc.

The statistics may be updated each time a new MAC packet is received anddecoded by the AP.

Next, at step 801, the AP determines a maximum waiting time between twosuccessive SP trigger frame transmissions.

The determination is based on the updated statistics, and may beperformed using pre-computed abacus of the optimal waiting time betweentwo successive SP TFs. To be more precise, the abacus may draw anoptimal waiting time as a function of the number of nodes in the networkand/or as a function of a collision rate (number of collided RUs out ofthe total number of RUs during the last N TXOP).

Note that different abacus may be used for different AP profiles: forinstance one abacus for an AP acting as a hot spot, one for an AP actingas a home set top box, one for an AP acting as an enterprise AP, etc.This is to better match with network conditions.

In a variant, the time interval between two successive SP TFs may bedetermined using a learning mechanism. For instance, the AP has receivedsmall packets from some nodes during the previous TXOPs.

The ratio of used RUs and the number of small packets received asdetermined during step 800 may be used to change the schedulinginterval. For instance, if a given threshold of RUs is used (typically80%), the AP may reduce the interval between two SP TFs by dividing acurrent time interval by a ratio, typically by two. On the contrary, asmall usage ratio of the RUs (less than 50%) may drive to increase theinterval between two SP TFs by multiplying the current time interval bya ratio, typically by 2.

While two mechanisms (abacus usage and learning mechanism) are suggestedabove, any other mechanism may be used to adapt the scheduling of the SPTF sending.

Next to step 801 having determined the maximum waiting time, step 802consists for the AP to schedule the next time instant at which the nextSP TF should be emitted. Thus, the AP adapts the delay until the next SPTF must be sent, based on the sending time of the previous SP TF and themaximum waiting time determined at step 801.

Steps 801 and 802 thus define a SP TF timer before sending a new SP TF.

Once, the next sending time instant is known, step 803 consists for theAP to determine when the delay/timer ends. If the delay has justexpired, a SP TF has to be sent and step 804 is executed. Otherwise, theSP TF timer value is modified or adjusted according to the delaydetermined at step 802 (if no timer is running, for instance during theactivation phase, a new timer is initiated with the waiting value), andthe system returns in the waiting step 799, waiting for a new packetreception.

When the SP TF timer has expired as detected either through test 803 ortest 799, step 804 is executed.

At step 804, the AP determines the characteristics of the SP TF: forinstance the number of RUs, and which ones are Scheduled RUs and whichones are Random RUs; the number of RUs allocated to small packets, andwhich ones from all the RUs; the TXOP duration; the maximum size oroverhead defining the small packets for the current SP TF.

For instance, the AP may adjust the predetermined maximum small packetsize or maximum overhead from one trigger frame to the other, based onnetwork statistics on one or more previous transmission opportunities.This information (maximum size or overhead) may be specified within theAP for the nodes to know the upper limit of the small packets.

Also, the AP may determine the number of resource units forming thecommunication channel, based on network statistics on one or moreprevious transmission opportunities. Again, this is to optimize usage ofthe network bandwidth given the nodes' needs.

In a first embodiment, the number of resource units, the predeterminedmaximum small packet size or maximum overhead and the TXOP duration arefixed and known by all the nodes. Step 804 only retrieves these values.For instance, a maximum small packet size is set, typically to 256bytes; the number of RUs dedicated to small packets is equal to thetotal number of possible RUs (typically 9 RU per 20 MHz channel) in thecomposite channel (typically 40 Mhz composite channel will contain 18RU); and the TXOP duration is set to fit the predefined maximum smallpacket size given the number of RUs.

In a more complex second embodiment, step 804 uses predefined abacus toobtain a value for those TF characteristics.

For instance, the number of RUs dedicated to small packets may be setaccording to a predefined abacus (typically linking the number of SP RUsto the number of nodes in the cell depending on the AP type: hot spot,home, enterprise, etc.).

A similar mechanism may be used to determine the maximum small packetsize.

Again, the TXOP duration may be set to fit the abacus-based maximumsmall packet size given the abacus-based number of RUs.

The abacus may be determined using simulation models or real measurementduring evaluation tests of the access point implementing the invention.

In a third embodiment, a learning mechanism is used during step 804 todetermine the TF characteristics.

For instance, the number of RUs dedicated to small packets may bedetermined as a function of the ratio of used RUs during the last TXOPdedicated to small packets. The ratios of used RUs, collided RUs and/orunused RUs are gathered at step 800. Based on such rations, a typicalalgorithm may be performed at step 804 to determine the number of smallpacket RUs: if the ratio of used RUs is more than 80%, the maximumnumber of SP RUs is doubled; if the ratio is less than 50%, the maximumnumber of SP RUs is divided by two; otherwise, the maximum number of SPRUs is unchanged.

Note that the number of RUs per 20 MHz should not exceed a maximumnumber of RUs, typically nine RUs per 20 MHz channel. Such value (9 RUsper channel) may be used by the AP as a default value when starting thewireless network cell.

Of course, combinations of these embodiments may be contemplated withinthe scope of the present first embodiments: for instance, a fixedmaximum small packet size and a number of SP RUs determined dynamically.

Next to step 804, step 805 creates and sends the SP trigger frame havingthe characteristics determined at step 804. This SP TF sending causesone or more nodes of the network to transmit their pending small packetsin Random RUs during the SP TXOP. Step 805 also launches a new SP TFtimer initiated with the current waiting interval value.

FIG. 9 illustrates an exemplary process for the node to process TriggerFrames, in particular TF dedicated to collection of small packets (SP).

At step 900, the node waits until a MAC packet addressed to it isreceived.

Upon receiving such MAC packet, the process goes to step 811 in whichthe node determines whether or not the received packet is a SP triggerframe.

To do so, the node checks, at step 901, whether or not at least one RUdefined by the TF is dedicated to small packets, by reading theappropriate restricting indicator in the TF (for instance the RU traffictype field 1521—see FIG. 15).

If it is not, the received MAC packet is processed according toconventional mechanisms, and the process loops back to step 900. Inparticular, in case the AP has sent a trigger frame with no indicationof small packet collection but with a very short TXOP to force the nodesto only send small packets, the node performs a conventional processing,meaning that it will looks for appropriate (small packet) data in itstransmitting buffer queues.

If the received packet is a SP TF, step 902 is executed during which thenode determines whether or not it has some small packets to transmit.

To do so, the node first determines the maximum small packet size oroverhead ratio. Depending on how the SP TF characteristics are definedas described above with reference to step 804, this maximum small packetsize or overhead ratio can be known in advance (fixed parameter), ortransmitted in the SP TF (through field 1522 of each RU for instance—seeFIG. 15).

As conventionally known, 802.11 nodes usually have a plurality ofordered transmitting queues (or Wi-Fi Multimedia (WMM) waiting queues).The queues are usually associated with traffic classes or accesscategories as mentioned above. Each WMM waiting queue is associated witha dynamic priority value which is usually an AC backoff counter.

During step 902, the node builds a list of small packets (SP list) to besent.

In a first embodiment, only the first (according to a transmission orderin the queue) small packet from the WMM transmitting queue having thehighest priority value (i.e. with the smallest backoff counter), giventhe maximum small packet size or overhead, is considered. So, a singlesmall packet is added to the list and thus sent by the node during thecurrent SP TXOP.

In a second embodiment, the first small packet from each WMMtransmitting queue, given the maximum small packet size or overhead, isconsidered. So, a maximum of four small packets (in case of the four802.11 WMM queues) is added to the list and thus sent during the currentSP TXOP.

In a third embodiment, all the small packets from all the WMMtransmitting queues, given the maximum small packet size or overhead,are considered.

In a fourth embodiment, in addition to the four existing 802.11 WMMqueues, the node may maintain a fifth transmitting queue in which itqueues only small packets (given the maximum small packet size oroverhead) as they are generated from transmission. In this embodiment,all the packets of the fifth transmitting queue storing only smallpackets are considered.

Once the SP list has been built, step 903 determines whether the SP listis empty or not (i.e. are there one or more small packets to transmit?).

If the SP list is not empty, step 904 is executed. Otherwise, theprocess loops back to step 900.

At step 904, the node selects one or several RUs to transmit all or partof the small packets of the SP list.

In a first embodiment, only one RU is selected, for instance one RandomRU among the SP RUs using the random allocation procedure 500 of FIG. 5.

In a second embodiment, if the SP list contains a plurality of packets,a plurality of RUs may be selected (e.g. a Random RU), for instance oneRU per packet of the SP list. However, several packets per RU can alsobe contemplated.

For illustrative purposes only, one RU per packet may be selected forthe first and second embodiments described at step 902. In thisconfiguration, the TXOP duration is preferably short so that the SP RUsare designed to fit more or less the maximum small packet size. Thisreduces the amount of padding.

Still for illustrative purposes, a number of RUs allowing thetransmission of all the small packets of the SP list (in one or severalRUs if needed) may be selected for the third and fourth embodimentsdescribed at step 902.

If a plurality of RUs is to be selected, a random allocation procedureis applied, for instance the procedure 500 described above withreference to FIG. 5 is applied iteratively to select all the requiredRUs.

Next to step 904, the node transmits the small packets of the SP list inthe selected RU or RUs, at step 905.

In the first and second embodiments described above at step 902, eachsmall packet of the SP list may be sent on a different RU.

In the third and fourth embodiments described above at step 902, thesmall packets are for instance aggregated (or concatenated) to fill inthe selected RU or RUs, according to the TXOP duration. When smallpackets are aggregated, the TXOP duration may be of conventional timelength because several small packets are sent within a single RU. Theaggregation thus helps reducing the amount of padding.

Next to step 905, the process loops back to step 900.

Turning now to FIGS. 10 and 11, they illustrate, using two flowcharts,general steps of embodiments of the present invention which restrictdata to be sent on at least one of the resource units to data having arestricted type of data, in particular to a specific traffic type ofdata. Traffic types of data generally refers to the four accesscategories defined in the 802.11 standard, namely AC_BK for backgrounddata, AC_BE for best-effort data, AC_VI for video applications and AC_VOfor voice applications. FIGS. 10a and 10b are alternative flowchartsfrom the Access Point's perspective, while FIG. 11 is a flowchart fromthe node's perspective. They apply to multi-user OFDMA uplink in an802.11ax wireless medium.

FIG. 10a illustrates an exemplary process for the AP to generate aTrigger Frame causing transmission of some traffic types (TT) by thenodes, also referred below to as TT Trigger Frame or TT TF. In thisexemplary process, the sending of the TT trigger frame is driven by thenumber of reserved RUs (test 1003 below).

During the initialization of the AP, the number of RUs to be allocatedduring an OFDMA transmission is predetermined at step 1000. This numbercan be fixed or dynamically updated. Various frequency widths may becontemplated for the RUs within the same composite channel, as describedbelow with reference to the embodiments of FIGS. 12 to 14.

Once the number of RUs is known, step 1001 consists for the node ingathering some statistics about the wireless network during one or moreprevious TXOPs. As described below, these statistics will be used todefine the traffic policy through which each RU to be reserved isassociated with a traffic type.

Several events and statistics can be tracked by the AP, for instance:

-   -   a collision ratio (of colliding RUs). Such ratio corresponds to        a percentage of bandwidth loss due to collisions among the nodes        of the 802.11 network cell.

When there are many collisions, many nodes contend for access thewireless medium at the same time. As a consequence, bandwidth sharingdriven by the AP can make the wireless access more fluent. So, forinstance, when the collision ratio is greater than a predeterminedthreshold, one or several TT trigger frame can be sent;

-   -   statistics regarding traffic types (for instance the four 802.11        access categories). An example of statistics is the part of each        traffic type among the overall amount of data sent by the nodes.        It corresponds to network statistics on the amount of data        received in one or more previous transmission opportunities for        each of the predefined traffic types. Note that

It is for the AP to assign a RU traffic type to each RU of the TTtrigger frame based on the part of each traffic type in the overalltraffic. A trigger frame profile may thus be generated and adapted,later on, as the network traffic evolves (due to evolving trafficrequirements such as the latency of each data traffic);

-   -   a queue size associated with each traffic type representing the        sum of all corresponding traffic waiting to be sent by all the        nodes.

As known in the 802.11 standard, the MAC header of the send packetincludes a “Queue Size” field indicating the amount of buffered trafficfor a given traffic type that is waiting in the transmitting node. Basedon such information, the AP is able to compute global statistics ontotal queue size for each of the predefined traffic types, a total queuesize for a predefined traffic type summing the sizes of transmissionqueues that are associated, in the nodes, with the predefined traffictype. The AP may then build an associated TT trigger frame defining RUswith dedicated traffic types.

Next to step 1001, step 1002 uses the statistics to dedicate one or moreRUs to respective specific RU traffic types.

When all the RUs of a trigger frame have been reserved for dedicatedtraffic types (in a variant when a predetermined number of RUs have beenreserved for dedicated traffic types) (test 1003), the trigger frame isbuilt and broadcasted to all the nodes (1004 and 1005).

FIG. 10b is a variant to FIG. 10a when the trigger frame is periodicallysent. In FIG. 10b , the sending of the TT trigger frame is no longerdriven by the number of reserved RUs (test 1003 below), but by thetraffic policy and mainly by the latency of traffics.

Based on statistics (including latency associated with each of the four802.11 standard access categories [voice, video, best effort,background] that have different requirements about latency—step 1011),the AP may determine at step 1012 a time interval before sending thenext TT Trigger Frame, also depending on which traffic types will beassociated with the RUs of the TT Trigger Frame. As the most criticalaccess category is the video access category, the time interval will beshorter for such a TT Trigger Frame including Video Access RUs than fora TT Trigger Frame including RUs only of the other access categories.

In a second sub-process, the AP waits for the end of the determined timeinterval (test 1013), and then prepare the TT Trigger Frame (step 1004)before sending it (step 1005).

FIG. 11 illustrates an exemplary process for the node to process TriggerFrames, in particular TT Trigger Frame sent by an AP according to FIG.10a or 10 b.

Upon receiving a TT trigger frame, i.e. a trigger frame defining one ormore RUs associated with restricting traffic types (test 1100), the nodechecks whether it is a TT Trigger Frame indicating a single restrictingtraffic type or not (test 1101).

If only one restricting traffic type is defined in the TT Trigger Frame,the node selects the corresponding access category WMM queue (step1120).

Next, it checks (step 1121) whether or not there is at least one packetready to be sent in the selected AC WMM queue. In such a way, the nodeselects data in a transmitting queue storing data having only thedetermined restricted type of data.

If there is one or more packets in the selected AS WMM queue, the nodeselects (step 1122) one (or more) RU having the restricting traffictype, for instance by using the procedure 500 of FIG. 5 to select oneRandom RUs associated with the restricted traffic type.

Next, the node transmits MPDU frames with the packets of the selected ASWMM queue, in the selected RU or RUs (step 1123) and waits for acorresponding acknowledgment from the AP indicating a successfultransmission (step 1124).

If two or more restricting traffic types are defined in the TT TriggerFrame (mixed traffic type), the node successively considers thetransmitting queue according to an highest-to-lowest priority valueorder, until data is sent on a resource unit; and for each transmittingqueue successively considered, it determines whether a resource unit inthe communication channel has the restricted traffic type, and in caseof positive determination, transmits data from the transmitting queuecurrently considered on the determined resource unit.

As shown in the Figure, the node first selects the access categoryhaving the (next) highest priority, i.e. the access category having thecurrent smallest backoff value (step 1110).

Next, the node parses the list of RUs as defined in the received TTTrigger Frame in order to select an RU having the same traffic type asthe (next) highest priority (step 1111).

If a single RU having the (next) highest priority traffic type isdetected, it is selected (step 1122).

In case several RUs have the appropriate traffic type, a randomallocation procedure as procedure 500 of FIG. 5 may be used to selectone particular RU (step 1122).

Once an RU has been selected, steps 1123 and 1124 described above areexecuted to perform data transmission.

If no RU defined in the TT TF has a dedicated traffic type matching the(next) highest priority traffic type, it is determined if anon-processed access category remains (step 1112), in which case theprocess loops back to step 1110.

Thanks to the restriction of RUs to specific traffic types, the AP mayefficiently adapt the TXOP to the various types of traffic.

Turning now to FIGS. 12 and 13, they illustrate, using two flowcharts,general steps of embodiments of the present invention in which theTrigger Frame define resource units within the communication channelthat have different frequency widths, i.e. a different number of tones.

FIG. 12 is a flowchart from the Access Point's perspective, while FIG.13 is a flowchart from the node's perspective. They apply to multi-userOFDMA uplink in an 802.11ax wireless medium.

FIG. 12 illustrates an exemplary process for the AP to generate aTrigger Frame defining resource units within the communication channelwith different RU frequency widths.

The process starts at step 1200 in which the AP gathers statistics onthe traffic in the network cell (BSS), for instance statistics regardingeach traffic type (for instance the four 802.11 access categories—video,voice, background, best effort). An example of statistics is the part ofeach traffic type among the overall amount of data sent by the nodes.Other statistics may include the number of registered nodes, themodulation scheme (MCS) used by each node, the modulation scheme (MCS)used on each RU, an identification of steady traffic (video streaming,VoIP . . . ) or random traffic (Web browsing, control frame . . . ), themean duration of transmission (without padding i.e. the duration for atransmission outside multi-user OFDMA uplink transmission or in amulti-user OFDMA uplink transmission by excluding padding duration).

Next, at the step 1201, the AP determines the number of concurrent (i.e.simultaneous) nodes and/or traffic types.

The number of concurrent nodes/traffics is used by the AP to define thenumber of RUs to allocate for the MU UL TXOP. For instance, the higherthe number of simultaneous nodes/traffics, the higher the number of RUs.

For illustrative purpose, the number of RUs may be set equal to thenumber of active nodes (i.e. transmitting data) in the N previous TXOPs(possibly TXOPs implementing the present embodiment of FIGS. 12 and 13).This approach is used for instance when each node can only sends data ofa single traffic type. It may also apply in the case the nodes areforced to send data of only one traffic type.

In any case, a traffic type is associated to each RU.

Step 1202 thus consists in reserving RUs in the TF for specific nodes ortraffics.

Note that the RU allocation of step 1202 should preferably take intoaccount the number of concurrent data traffics within each node, since acorresponding number of RUs should be provided for the specific node, ifat all possible. For instance, a node may transmit two separate datatraffics through the AP: a video stream may coexist with a VoIPcommunication in a smartphone.

As a consequence, the number of RUs may be set equal to the number ofpairs (traffic type, transmitting node) detected during the N previousTXOPs (possibly TXOPs implementing the present embodiment of FIGS. 12and 13).

Step 1202 thus defines an optimal number of RUs that should be providedto satisfy the network needs, each RU being dedicated to a respectivetraffic type. Note that this optimal number of RUs is not necessarilycorrelated to the real number of available RUs at this stage of theprocess (it means that the optimal number may be higher than the numberof possible RUs in the composite channel).

Next, steps 1203 and 1204 are executed in relation with each other andmay be looped to avoid inconsistency to define the duration of the TXOPor the number of RUs and corresponding frequency widths first, and theother in relation to the information first defined.

At step 1203, the AP computes the duration of the next MU ULtransmission, i.e. the next TXOP triggered by the trigger frame to besent.

To do so, the AP determines which types of data traffic are currentlyconveyed in the network (based on statistics on previous N TXOPs forinstance or on the traffic types associated with the RUs determined atstep 1202) and more especially the repartition of data traffic, forinstance according to the four 802.11 ACs, in order to adjust the TXOPduration accordingly.

More generally, the duration may be determined according to the averageduration of N (integer) previous transmissions in order to minimizingthe padding on average.

In a variant, the duration may also be determined to give priority tosome traffic. For instance, if a lot of best effort traffic is conveyedin the RUs during one or more previous TXOPs, a short TXOP duration maybe chosen, for instance by taking the time allowing the transmission ofthe typical quantity of data of the best effort access category(according the statistics obtained in 1200). On the contrary, if severalvideo streams are on-going, a larger TXOP duration may be chosen,preferably close to the TXOP limit defined for the video accesscategory.

Without any statistic, the TXOP duration may be set to of the TXOP limitduration of the video access category (AC_VI) and accordingly one RUwith a 106 tones width is allocated for video—AC_VI (or traffic withlarge quantity of data to transmit), one RU with a 52 tones width isallocated for VoIP—AC_VO (or traffic with intermediate quantity of datato transmit) and three RUs with 26 tones each, are allocated forrespectively Best effort, Background access category (AC_BE, AC_BK) andcontrol packet in a 20 MHz channel, i.e. one RU per each traffic type onthe 20 MHz band.

Once the TXOP duration has been determined, the AP defines, at step1204, the RU characteristics for the next TXOP.

This includes the number of RUs. Furthermore, as the TXOP duration isset, the other main RU characteristic to be determined is the frequencywidth (number of tones) for each RU forming the TF.

According to the TXOP duration and the quantity of data to transmit foreach traffic type (list of the optimal RU allocation and associatedquantity of data), the AP determines the frequency width of each RU (foreach traffic type) in term of tones (the quantity of data to transmitbeing a function of the TXOP duration and of the RU_(—) width_(—) in_(—)tones).

Next, the AP decides how to allocate the tones available on thecomposite channel to various RUs, in order to define the TF. This takesinto account the RU_width_in_tones for each traffic type.

For instance, four RU_width_in_tones may be defined for a channel of 20MHz (26 tones, 52 tones, 106 tones and 242 tones).

For a 20 MHz channel in OFDMA MU Uplink, the maximum number of RUs withrespect to the definition of the RU_width_in_tones may be defined asfollow: nine RUs of 26 tones each; or four RUs of 52 tones each plus oneRU of 26 tones; or two RUs of 106 tones each plus one RU of 26 tones; orone RU of 242 tones. These are exemplary RU profiles among a wide set ofpossible RU profiles. The only limitation to mix the differentRU_width_in_tones is the maximum number of tones for a channel (e.g. for20 MHz, 242 tones).

Back to the previous RU profile example, the AP may allocate forinstance three RUs of 26 tones plus one RU of 52 tones plus one RU of106 tones in a channel of 20 MHz.

If the number of required RUs defined at step 1202 as the optimal numberof RUs is higher than the capability of the composite channel given theRU_width_in_tones for each traffic type, a prioritization is performed.It can be made based on the traffic categories, to give priority tosteady streams, small packets, or to minimize as much as possiblepadding by excluding the RU or RUs for which the actual transmissionduration of useful data (by taking into account the modification ofduration applied by the number of tones allocated) is very differentfrom the TXOP duration defined in the previous step. These RUs are thosefor which too few data are scheduled for transmission.

After, the allocation and the definition of the RU characteristics, theTXOP duration can be refined (if necessary) to adjust the transmissionduration with the effective RU slots.

The RU frequency width is preferably determined based on the traffictype to which it is dedicated as determined at step 1202 based onstatistics. That is the frequency width of the resource units isdetermined based on statistics on data related to each traffic type asreceived in one or more previous transmission opportunities. Note thatthe RUs may be explicitly assigned to a specific traffic type in the TF,using the mechanisms described above with reference to FIGS. 10 and 11.

However, the specific traffic type may not be signalled in the TF. Thisis because, by designing the RUs with appropriate sizes, the nodes willselect data that fit well the available bandwidth of the RUs, i.e. theintended content (traffic type) is implicitly designated. For instance,RUs with large frequency width are implicitly dedicated for largecontents such as video.

An example of RU frequency widths is the following: the AP allocates 4times more tones to a video RU_traffic_type than to a backgroundRU_traffic_type and 2 times more tones to a voice RU_traffic_type thanto a background RU_traffic_type in order to keep the differentiationbrought by the TXOP Limit parameter of the 802.11n standard. In otherwords, the resource unit or units associated with AC_BK and AC_BEtraffic type have a first frequency width (for instance the minimalfrequency width authorized by the 802.11 standard, i.e. 2.03 MHz whenthe 20 MHz channel is split into nine RUs), the resource unit or unitsassociated with AC_VO have a frequency width equal to twice the firstfrequency width and the resource unit or units associated with AC_VIhave a frequency width equal to four times the first frequency width.

Due to the 1/4 ratio of the frequency width between AC_BK RUs and AC_VORUs, the TXOP duration is preferably set less or equal to a quarter ofthe TXOP Limit parameter set for the wireless network according to the802.11 standard.

For illustrative purposes, the 802.11n standard defines a TXOP Limit of3.008 ms for the video access category (AC_VI), 1.504 ms for the voiceaccess category (AC_VO) and 0 ms (i.e. 1 MPDU) for the background andbest effort access categories (resp. AC_BK and AC_BE). When implementingthe present embodiment, the AC_BK and AC_BE may be defined with theminimum number of tones (e.g. 26 tones), the AC_VO with twice moretones, i.e. 52 tones and the AC_VI with four times more tones, i.e. 106tones. For this configuration the duration of the MU UL transmission,thus defining the TXOP duration, is set to 752 μs (3.008 ms/4).

Furthermore, the frequency width (number of tones) for an RU may alsodepend on the modulation scheme, MCS (which also impact the transmissionduration) used by the node to reach the AP (an MCS may be defined byeach node, but also per RU in each node). In other words, the frequencywidth of a resource unit associated with a traffic type is adjustedbased on a modulation scheme used by the nodes to send data having theassociated traffic type in one or more previous transmissionopportunities.

On the other hand, the AP may also set the MCS to use in order tominimize padding and to maximize BER.

Once all the RU characteristics are known, the TF can be generated andsent on the network at step 1205. A signalling of some RUcharacteristics in the TF is further described below with reference toFIG. 15.

Note that, for Random RUs, the TF should signal at least the TXOPduration, the number of Random RUs and the frequency width(RU_width_in_tones) for each Random RU. If an RU is explicitly dedicatedto a specific traffic type, it is signalled in the TF using aRU_traffic_type field. The latter may be substituted to theRU_width_in_tones if the number of tones is fixed per traffic type.

Next to the TF sending, the AP waits, at step 1206, for the end of theTXOP and sends an acknowledgment (1207), if appropriate, to acknowledgereception of all or part of the MPDUs transmitted from multiple userswithin the OFDMA TXOP.

Preferably, the ACK frame is transmitted in a non-HT duplicate format ineach 20 MHz channel covered by the initial TF's reservation.

Next, at step 1208, the AP updates its statistics according to thecurrent transmission.

FIG. 13 illustrates an exemplary process for the node to process TriggerFrames, in particular the Trigger Frame sent by an AP according to FIG.12.

At step 1300, the node detects a trigger frame reserving a compositechannel. The TF is then decoded in order to analyse its content. The TFdefines a plurality of RUs.

At step 1301, the node selects one (or more) of the RUs using the RUcharacteristics specified in the TF. The selection may also be based onthe traffic types it has to transmit.

The node selects any Scheduled RU corresponding to its node_AID anddetermines the possible traffic_type associated with the Scheduled RU ifany. This is to send appropriate data in the RUs.

For Random RUs, the node selects one (or more) Random RU:

either having a signalled traffic type corresponding to a traffic typethe node has to transmit (for instance the priority AC queue). This isto drive the node to transmit, on one resource unit, data having thesame traffic type as the traffic type associated with the resource unit,

or having a frequency width in tones that matches, given the TXOPduration, as much as possible the amount of data it has to transmit (forinstance from the priority AC queue). It means that the node determinewhether or not one of the resource units matches the amount of data tobe sent in the transmitting queue having the highest priority value, andonly in case of positive determining, it transmits the data of thetransmitting queue having the highest priority value on the matchingresource unit.

The node may also use other information from the TF, such as MCS, toadjust its transmission parameter.

Next, at optional step 1302, the node may adapt or adjust a modulationscheme for modulating the data on the resource unit (possibly resourceunits), the adapting maximizing the time duration of transmitting thedata within the transmission opportunity. This step of reducing the MCSseeks to minimize padding in relation to the TXOP duration for the nextMU UL transmission. However the same amount of data is transmitted, butwith a better BER.

Next, at step 1303, the node transmits the data on the respective one ormore RUs selected at step 1201.

At step 1304, the node waits for an acknowledgement from the AP.

When a successful transmission acknowledgment is received, the nodeflushes the buffered data from the AC transmitting queues at step 1305,ending the process.

FIG. 14 illustrates the benefits of the embodiment of FIGS. 12 and 13,in terms of padding reduction, compared to the situation of FIG. 5a .The benefits rely on choosing different RU profiles according to datatraffic and/or node characteristics.

As shown in the Figure, the AP sends a TF with RUs having differentfrequency widths (in tones number) and having a shorter TXOP duration550′ compared to FIG. 5a . In other words, the AP modifies bothdimensions of the RUs (TXOP duration and frequency width in tones) tooptimize padding.

In the example of the Figure, the PPDU of node STA4 comprise the sameamount of data between FIG. 5a and FIG. 14. However, as the used RU inFIG. 5a is composed of 26 tones and the used RU in FIG. 14 is made of 80tones, the TXOP duration is substantially reduced, namely divided byabout 3 in this example.

On the other hand, the nodes that where sending a lot of padding in FIG.5a (more than 50% of the MU UL duration) e.g. STA1, STA2, STAG, nowsends a substantially reduced amount of padding, thanks to the reductionof the TXOP duration (itself made possible thanks to the various RUfrequency widths).

Note that the nodes to which no RU has been allocated (STA3, STA7 andSTA8 cannot transmit in this MU UL OFDMA transmission) will transmit ina next MU UL transmission or through a conventional access to thewireless medium (EDCA).

The embodiment of FIGS. 12 and 13 may be applied to both Random RUs andScheduled RUs.

Random RUs may be used at the creation of the network cell driven by theAP, before Scheduled RUs are used.

Initially, predefined statistics defining a proportion of the differenttraffic types in a cell and a typical number of nodes in a cellaccording to the AP characteristics (office, home, stadium . . . ) maybe used to define the initial number of Random RUs. TXOP duration andthe RU frequency widths may be defined by keeping the scale factor ofthe 802.11 standard, for instance the AC_BK and AC_BE are defined with26 tones, the AC_VO with 52 tones and the AC_VI with 106 tones, whilethe MU UL transmission duration is set to 750 μs.

The initial Random-based phase may be a transitory step used as alearning phase to learn about the traffic type or types sent by eachnode, the modulation used by each node and/or on each RU, etc. beforethe Scheduled-based mode is used. In other words, it is a phase duringwhich the node collects or gathers statistics as those mentioned abovewith reference to step 1200.

During the learning phase, the Random RUs may be dynamically adjusted orrefined based on the statistics dynamically gathered. This is toprogressively modify the RUs to mirror the real traffic proportions andthe number of active registered nodes.

A result of the learning phase is that the width of each RU and theallocation of each RU to a dedicated node can be defined preciselyaccording to current network usage. Preferably, the RU frequency widthis chosen based on traffic types, but also based on the modulationscheme because the latter can greatly modify the transmission durationrequired for a fixed data quantity (for instance modulation MCS 0provides a bitrate of 6.5 Mbps, while modulation MCS 1 provides abitrate of 13 Mbps).

Next, the Scheduled RU mode is used where the AP explicitly allocatesthe designed RUs to specific nodes based on node's needs (for instancetransmitted during a previous TXOP; or the AP may use trafficspecification, e.g. TSPEC in HCCA, supplied by some nodes to definetheir need).

FIG. 15 presents the format of a ‘RU Information Element’ (1510), whichmay be used to signal small packet attributes of the TF and/ortraffic_type attributes of the TF and/or RU frequency width attributes.

The ‘RU Information Element’ (1510) is used by the AP to embedadditional information inside the trigger frame related to the OFDMATXOP. It format preferably follows the ‘Vendor Specific informationelement’ format as defined in the IEEE 802.11-2007 standard.

The ‘RU Information Element’ (1510) is a container of one or several RUattributes (1520), having each a dedicated attribute ID foridentification. The header of RU IE can be standardized (and thus easilyidentified by the nodes) through the Element ID, OUI, OUI Type values.

The RU attributes 1520 are defined to have a common general formatconsisting of a one-byte RU Attribute ID field, a two-byte Length fieldand variable length attribute specific information fields.

The usage of Information Element inside the MAC frame payload is givenfor illustration only, any other format may be supportable.

The choice of embedding additional information in the MAC payload isadvantageous for keeping legacy compliancy with the medium accessmechanism, because any modification performed inside the PHY header ofthe 802.11 frame would have inhibited any successful decoding of the MACheader by legacy devices.

As shown in the Figure, a dedicated RU attribute follows the followingformat:

-   -   The Attribute ID is a dedicated value identifying the ‘RU Info’.        A value unused in the standard, e.g. in the range 19-221, may be        selected. This one-byte value is a tag starting the ‘RU Info’.    -   A two-byte length field defining the length of the attribute        body.

The attribute body varies according to the embodiments considered.Attribute body 15 a refers to the small packet embodiment of FIGS. 8 and9; attribute body 15 b refers to the traffic type embodiment of FIGS. 10and 11; and attribute body 15 c refers to the varying RU widthembodiment of FIGS. 12 and 13.

To efficiently signal the small packet mode (FIGS. 8 and 9), theattribute body 15 a for a given RU (or for the whole TF) may include:

an SP type field 1521 to indicate if the RU (or all the RUs) isrestricted to small packets (or if the TF is a SP TF). This field set tothe SP type (small packet type) indicates to the receiving node that theRU (or all the RUs) can only be used to send small packets, for instancesmaller than a maximum small packet size;

a maximum small packet size field 1522 used by the AP to explicit definea maximum size for the small packets.

To efficiently signal the traffic type mode (FIGS. 10 and 11), theattribute body 15 b may include:

a TF_type field 1523 to indicate if the Trigger Frame specifies themixed mode of step 1101 or not (i.e. specifies a list of RUs with thesame traffic type or a list of RU with different mixed traffic types);

an RU_nb field 1524 to define the number of Resource Units composing thecomposite channel. This number also gives the number of entries in thenext field;

an RU_list field 1525 listing the characteristics of each RU of thecurrent OFDMA TXOP. Each entry in the list 1525 may include thefollowing set of field:

an RU_index field to specify the index of the current RU in the RU list;

an RU_type field to specify the Random or Scheduled mode of the RU (onlyin case of mixed mode);

an RU_traffic_type field to specify the traffic type supported by theRU; and

an optional Node_AID field to define the identifier of a node in case ofa Scheduled RU. This could be the MAC address, or the AssociationIdentifier (AID), or the Partial AID of a node.

To efficiently signal the RU frequency widths (FIGS. 12 and 13), theattribute body 15 c for a given RU may include:

an RU_nb field 1524 to define the number of Resource Units composing thecomposite channel. This number also gives the number of entries in thenext field;

an RU_list field 1525 listing the characteristics of each RU of thecurrent OFDMA TXOP. Each entry in the list 1525 may include thefollowing set of field:

an RU_index field to specify the index of the current RU in the RU list;

an RU_width_in_tones field to specify the number of tones for this RU;

an RU_type field to specify the Random or Scheduled mode of the RU (onlyin case of mixed mode);

an RU_traffic_type field to specify the traffic type supported by theRU;

an optional MCS field to specify the modulation scheme to use for theRU; and

an optional Node_AID field to define the identifier of a node in case ofa Scheduled RU. This could be the MAC address, or the AssociationIdentifier (AID), or the Partial AID of a node.

All or part of the various attribute bodies described above may becombined to define for instance an SP Trigger Frame which is also a TTTrigger Frame with RUs having varying frequency widths.

Although the present invention has been described hereinabove withreference to specific embodiments, the present invention is not limitedto the specific embodiments, and modifications will be apparent to askilled person in the art which lie within the scope of the presentinvention.

Many further modifications and variations will suggest themselves tothose versed in the art upon making reference to the foregoingillustrative embodiments, which are given by way of example only andwhich are not intended to limit the scope of the invention, that beingdetermined solely by the appended claims. In particular the differentfeatures from different embodiments may be interchanged, whereappropriate.

In the claims, the word “comprising” does not exclude other elements orsteps, and the indefinite article “a” or “an” does not exclude aplurality. The mere fact that different features are recited in mutuallydifferent dependent claims does not indicate that a combination of thesefeatures cannot be advantageously used.

1-43. (canceled)
 44. A wireless communication method in a wirelessnetwork comprising an access point and a plurality of nodes, the methodcomprising, at the access point, the step of sending a trigger frame tothe nodes, the trigger frame reserving at least one communicationchannel of the wireless network for a transmission opportunity anddefining a plurality of resource units splitting the communicationchannel in the frequency domain, wherein the trigger frame includes oneindicator per resource unit, each indicator restricting data to be senton the respective resource unit to data having a restricted traffic typeof data.
 45. A wireless communication method in a wireless networkcomprising an access point and a plurality of nodes, the methodcomprising, at one of said nodes: receiving a trigger frame from theaccess point, the trigger frame reserving at least one communicationchannel of the wireless network for a transmission opportunity anddefining a plurality of resource units splitting the communicationchannel in the frequency domain, wherein the trigger frame includes oneindicator per resource unit, each indicator restricting data to be senton the respective resource unit to data having a restricted traffic typeof data; determining, from the trigger frame, an indicator defining arestricted traffic type of data authorized for at least one of theresource units; determining, from local transmitting memory, data havinga traffic type corresponding to the determined restricted traffic typeof data; and transmitting the determined data to the access point on thesaid resource unit.
 46. The wireless communication method of claim 44,wherein the restricted traffic type of data is one of the four accesscategories defined in the 802.11 standard, namely AC_BK for backgrounddata, AC_BE for best-effort data, AC_VI for video applications and AC_VOfor voice applications.
 47. The wireless communication method of claim45, wherein determining, from local transmitting memory, data having atraffic type corresponding to the determined restricted traffic type ofdata includes selecting data in a transmitting queue storing data havingonly the determined restricted traffic type of data.
 48. The wirelesscommunication method of claim 45, wherein the node's local transmittingmemory includes a plurality of transmitting queues, each beingassociated with a dynamic priority value and with a traffic type, andthe method further comprises: successively considering the transmittingqueue according to an highest-to-lowest priority value order, until datais sent on a resource unit, and for each transmitting queue successivelyconsidered, determining whether a resource unit in the communicationchannel has the restricted traffic type, and in case of positivedetermination, transmitting data from the transmitting queue currentlyconsidered on the determined resource unit.
 49. The wirelesscommunication method of claim 44, further comprising determining afrequency of sending a trigger frame having a restricted traffic typeindicator, based on network statistics on one or more previoustransmission opportunities.
 50. The wireless communication method ofclaim 44, further comprising determining the number of resource unitsforming the communication channel, based on network statistics on one ormore previous transmission opportunities.
 51. The wireless communicationmethod of claim 49, wherein the network statistics include one or morefrom: a number of nodes registered to the access point in the wirelessnetwork, a number of collisions or a collision ratio occurring duringthe one or more previous transmission opportunities, a distribution ofpacket sizes received by the access point, in particular a packet sizedistribution relative to a maximum packet size, an amount of datatransmitted by the nodes, an amount of data transmitted by the nodes foreach traffic type from among a plurality of predefined traffic types,and a ratio of medium busyness, for instance the ratio of a medium busytime on a given period (e.g. one second).
 52. The wireless communicationmethod of claim 44, wherein the trigger frame defines various restrictedtypes of data for various respective resource units.
 53. A wirelesscommunication method in a wireless network comprising an access pointand a plurality of nodes, the method comprising, at the access point,the step of: sending a trigger frame to the nodes, the trigger framereserving at least one communication channel of the wireless network fora transmission opportunity and defining a plurality of resource unitssplitting the communication channel in the frequency domain, theplurality of resource units having the same time length in the same timedomain; wherein resource units within the communication channel havedifferent frequency widths.
 54. A wireless communication method in awireless network comprising an access point and a plurality of nodes,the method comprising, at one of said nodes, the steps of: receiving atrigger frame from the access point, the trigger frame reserving atleast one communication channel of the wireless network for atransmission opportunity and a plurality of resource units splitting thecommunication channel in the frequency domain, the plurality of resourceunits having the same time length in the time domain, and transmittingdata to the access point on one of the resource units, wherein resourceunits within the communication channel have different frequency widths.55. The wireless communication method of claim 53, wherein each resourceunit is associated with a traffic type of data selected from the fouraccess categories defined in the 802.11 standard, namely AC_BK forbackground data, AC_BE for best-effort data, AC_VI for videoapplications and AC_VO for voice applications.
 56. The wirelesscommunication method of claim 55, wherein resources units associatedwith AC_BK and AC_BE traffic types have a frequency width equal to aminimal frequency width authorized by the 802.11 standard.
 57. Thewireless communication method of claim 54, wherein each resource unit isassociated with a traffic type of data, and the method furthercomprises, at the node: transmitting, on one resource unit, data havingthe same traffic type as the traffic type associated with the resourceunit.
 58. The wireless communication method of claim 53, wherein eachresource unit is associated with a traffic type of data, and the methodfurther comprises: determining the frequency widths of the resourceunits based on statistics on data related to each traffic type asreceived in one or more previous transmission opportunities.
 59. Thewireless communication method of claim 53, further comprisingdetermining the number of resource units forming the communicationchannel, based on network statistics on one or more previoustransmission opportunities.
 60. A communication device acting as anaccess point in a wireless network also comprising a plurality of nodes,the communication device acting as an access point comprising at leastone microprocessor configured for carrying out the step of sending atrigger frame to the nodes, the trigger frame reserving at least onecommunication channel of the wireless network for a transmissionopportunity and defining a plurality of resource units splitting thecommunication channel in the frequency domain, wherein the trigger frameincludes one indicator per resource unit, each indicator restrictingdata to be sent on the respective resource unit to data having arestricted traffic type of data.
 61. A communication device in awireless network comprising an access point and a plurality of nodes,the communication device being one of the nodes and comprising at leastone microprocessor configured for carrying out the steps of: receiving atrigger frame from the access point, the trigger frame reserving atleast one communication channel of the wireless network for atransmission opportunity and defining a plurality of resource unitssplitting the communication channel in the frequency domain, wherein thetrigger frame includes one indicator per resource unit, each indicatorrestricting data to be sent on the respective resource unit to datahaving a restricted traffic type of data; determining, from the triggerframe, an indicator defining a restricted traffic type of dataauthorized for at least one of the resource units; determining, fromlocal transmitting memory, data having a traffic type corresponding tothe determined restricted traffic type of data; and transmitting thedetermined data to the access point on the said resource unit.
 62. Acommunication device acting as an access point in a wireless networkalso comprising a plurality of nodes, the communication device acting asan access point comprising at least one microprocessor configured forcarrying out the step of sending a trigger frame to the nodes, thetrigger frame reserving at least one communication channel of thewireless network for a transmission opportunity and defining a pluralityof resource units splitting the communication channel in the frequencydomain, the plurality of resource units having the same time length inthe time domain; wherein resource units within the communication channelhave different frequency widths.
 63. A communication device in awireless network comprising an access point and a plurality of nodes,the communication device being one of the nodes and comprising at leastone microprocessor configured for carrying out the steps of: receiving atrigger frame from the access point, the trigger frame reserving atleast one communication channel of the wireless network for atransmission opportunity and a plurality of resource units splitting thecommunication channel in the frequency domain, the plurality of resourceunits having the same time length in the time domain, and transmittingdata to the access point on one of the resource units, wherein resourceunits within the communication channel have different frequency widths.64. A non-transitory computer-readable medium storing a program which,when executed by a microprocessor or computer system in a device of awireless network, causes the device to perform the wirelesscommunication method of claim 44.